BakuDeku

"From kindergarten to elementary school, to middle school and high school. The two of us have been together as long as I can remember, and yet... we've never exposed our true feelings and talked things out... not even once."

- Izuku Midoriya, Chapter 119.

BakuDeku is the slash ship between Katsuki Bakugou and Izuku Midoriya from the My Hero Academia fandom.

Canon
Izuku and Katsuki have known each other since a very young age, it being said many times throughout the series that they are childhood friends. Due to a series of misguided instances, their relationship deteriorated and became strained after many complications from their childhood, including Katsuki pushing Izuku away due to his fear of Izuku's spirit. Gradually, however, their friendship is repairing as they both mature and strive to resolve their issues - Katsuki even beginning to indirectly encourage Izuku to become stronger in some recent chapters. Despite their issues, Izuku continues to admire Katsuki for a multitude of things, especially his strength and ability as a hero, stating that Katsuki is his true "image of victory".

Originating from childhood, the pair use nicknames for each other, albeit mainly out of spite on Katsuki's half. Despite his general negativity towards Izuku, Katsuki allows Izuku to call him by the nickname "Kacchan", without objection. The suffix "-chan" is considered to be very cutesy and feminine, as it is primarily used to refer to young children, close friends, or people with a generally cute appearance, obviously contradicting Katsuki's brash and explosive nature. As shown explicitly throughout the series, especially considering Izuku, if Katsuki has a problem with something or someone he will be the first to make a comment about it; making it questionable why he has no issue with Izuku using the nickname. One theory is that the nickname is one of the small fragments of the pair's childhood that remains untainted, and so Katsuki holds onto it without posing an argument. The other instance where "Kacchan" has been used was by Kaminari in chapter 163, seemingly in a teasing way; to which Katsuki disregards entirely and leaves the room to go to bed. Horikoshi, the creator of the series, also refers to Katsuki as the nickname on occasion as seen throughout his sketches, but has not revealed much on its origin or history.

Izuku, on the other hand, receives the nickname "Deku" from Katsuki at a very early point in their relationship, which essentially translates to "useless person", referring to Izuku's quirkless state. Ironically, this eventually becomes Izuku's hero name through suggestion from his friend and classmate Ochako, who puts a positive spin on the name and tells him that it reminds her of the phrase "you can do it!". Katsuki is initially angered at this, internally believing it to be another way of Izuku mocking him, but makes no comment otherwise.

Ever since Izuku failed to develop a Quirk, Katsuki has seen Izuku as someone below him in terms of ability and general worthiness. This was reinforced as Katsuki developed his own Quirk and was constantly praised by his teachers and classmates for it, whilst Izuku was reprimanded for his lack thereof. Being an easily influenced child at the time, Katsuki noticed this dramatic difference in the way they were both treated, realising that Izuku was essentially a nobody in a world where Quirks so heavily define someone as a person. Holding onto the belief that he was going to be the best, Katsuki continued to view Izuku as nothing but a 'pebble' in his path towards becoming a hero, his intense attachment to victory manifesting itself into somewhat of a superiority complex.

Season 1
During the scene in which Katsuki falls into the river, Izuku runs down to help him. This offends Katsuki because Deku, the quirkless kid who was clearly below him, was supposedly looking down on him. Katsuki bullied Izuku for a number of years after this event, using Izuku as an outlet for his anger towards his strive to become the greatest hero. After finding out that Izuku also wanted to enter U.A's hero course, Katsuki was aggressive and mocked his choice, stating that he had no chance in becoming a hero and should instead "take a swan dive off the roof of the school”. Whilst this was said in an enraged stupor in front of his friends, Izuku still concerns for Katsuki's impulsive actions, stating that Katsuki would’ve gotten into trouble if Izuku had actually jumped off the roof. Later on, when Katsuki and his friends were in an alleyway, one of his friends tell Katsuki that he’d gone a bit too far that time, meaning that was not his usual behavior.

On his way home, Izuku sees an explosion and a crowd surrounding what appears to be another villainous incident, and soon discovers that a boy (Katsuki) had been captured by that same slime monster that All Might had saved Izuku from before. As his limbs were constricted and his mouth was covered, Katsuki struggled desperately to break free. The unbearable pain caused Katsuki to stare wide-eyed in despair. Izuku saw this and immediately rushed towards him without a second thought, despite how dangerous it was. With his quick thinking, he threw his backpack at the slime monster. His books flew out and one of them hit slime monster‘s eye, causing it to loosen up a bit and allowed Katsuki to gasp for air. Izuku then proceeded to claw frantically at the slime monster. Katsuki angrily asked why Izuku was there, and Izuku said it was due to his legs “moving on their own”, and that Katsuki looked liked he ”needed to be saved”. This spurs All Might and  the other onlooking Pro Heroes to intervene, saving the pair and defeating the villain.

After the sludge incident, as Izuku was walking home, Katsuki stopped him in his tracks and stated that he “didn’t need his help” and was “fine on his own”. He also told Izuku not to look down on him. Katsuki then turns and walks away, as Izuku watches him with a glad expression on his face. Upon their next meeting, instead of Katsuki harassing Izuku as per usual, he instead merely threatens him, acknowledging that Izuku's bravery saved his life, and in an indirect way, thanking him.

Izuku also mentioned that ever since this incident, Katsuki had never physically harassed him ever again.

After Izuku received the quirk One for All from All Might, their relationship became even more complicated through Katsuki's misunderstandings of the Quirk's origin.

During their first training session, Katsuki felt betrayed when he saw Izuku activating his newfound quirk during the ball throwing portion, believing that Izuku had been keeping his quirk a secret since they were children. He had to be restrained by Aizawa as he understandably charged at and demanded answers from Izuku. Having promised All Might that he would keep One for All a secret, Izuku had to leave Katsuki in the dark about the situation, unknowingly making Katsuki even more upset about being believably mocked and betrayed by his childhood friend.

Later on, after the Hero vs. Villain fight with All Might, it shows the guilt in Katsuki’s face when realizes that he took the fight way too far and how much he hurt Izuku in their first fight. Izuku wakes up at the nurse's room and returns to his classroom to find that Katsuki had left and rushes to find him, despite his friends telling him to wait. Izuku confronts him, assuring that he has never deceived him and spills the fact that his quirk is a ”borrowed power”, deciding not to mention All Might's involvement just yet. He states that he will however make this borrowed power his own and eventually surpass Katsuki by becoming stronger. This causes Katsuki, despite not understanding exactly what Izuku meant, to cry out in frustration, tears forming in his eyes as he yells at Izuku to buck up and train hard as well, determined that he will be number one. This is the first time we see Katsuki emotionally open up to Izuku despite their tainted past, and this theme continues under the influence of One For All.

Season 2
In season 2, episode 37, Izuku is paired up with Katsuki for their final exam to each other's dismay. At the start, Katsuki decides to take the lead and ignore Izuku's suggestions of pairing up and avoiding a fight with All Might, well aware of the true extent of his power. Disregarding the idea of backing down from a fight, Katsuki responds by saying that he'll score higher if he defeats All Might; reinforcing his desire to win. Izuku continues to argue against this, to which Katsuki angrily lashes out and punches him, resulting in Izuku landing backwards. As Katsuki walks away, demanding Izuku to not speak to him, Izuku tries once more to make him reconsider; resulting in them shouting at each other, Izuku angrily yelling that this is why they can never have "normal conversations." All Might then appears, using a Texas Smash down the main street, causing the pair to be blown away. Acting as the villain, All Might menacingly states that the two should take the exam seriously, causing them to react by attacking haphazardly in any way they can. As the exam relies on teamwork, it goes badly for the two of them as the fight progresses, All Might easily managing to outsmart and attack both students without bother.

After All Might pins Izuku under a fence and delivers a punch to Katsuki's gut, All Might tells Katsuki that he has much room for him to grow as a hero, understanding that he is infuriated by Izuku's sudden immense improvement upon gaining his Quirk. Weakly, Katsuki replies: "If you're saying I have to rely on [Izuku's] help, then I'd rather lose."

As All Might prepares to finish off Katsuki, Izuku breaks away from the fence in anger and punches Katsuki in the face, saying "Don't you say you'd rather lose!" He carries Katsuki away to an alleyway whilst All Might is distracted and admits to himself that he can't come up with a plan to pass the exam. As Katsuki is being carried, his mind repeats the words Izuku said to him, triggering a flashback to when the two when they were younger in which Katsuki is scaring away two older children after they caused trouble with him. Obviously scuffed up from the encounter, he scoffs that "the most amazing hero always wins in the end," as Izuku watches on in awe from behind a tree.

Back in the present day, Katsuki yells at Izuku to put him down, blasting out of his grasp. Annoyed at being reminded by his own words, he blasts the wall next to Izuku's shoulder in a kabedon-esque manner (anime only), stating that in order to escape they have to fight All Might.

Katsuki comes up with a plan to use maximum firepower on All Might in order to create distance between them. He firstly runs out of the alleyway and distracts All Might, who is initially unimpressed and believes it to be a sneak attack. Katsuki then cries out to Izuku, yelling for him to "shoot" as Izuku appears behind All Might and points at him with one of Katsuki's gauntlets. He fires the gauntlet at All Might, apologizing as he does so, catching him off guard. It appears that the plan had worked, seeing no trace of All Might after the collision, until he reappears unharmed and breaks both of Katsuki's gauntlets.

Another fight ensues, chipping away at Katsuki as his ability weakens through use of his Quirk sparing the gauntlets. At one point, All Might even goes as far as to using New Hampshire Smash directly into Izuku's back, causing him immense pain and emphasizing their struggle at this point in the battle. Katsuki, infuriatingly at terms with their current status in the battle, decides his last option is to throw Izuku towards the exit to gain their win. As All Might attempts to stop Izuku, Katsuki comes in to defend his teammate and blasts All Might, who avoids this attack and drags Katsuki to the ground.

Izuku, aware of Katsuki's state, runs back to rescue him so that they can pass together, successfully delivering an attack to All Might that allows him to sweep an unconscious Katsuki under his arm and aim for the exit. He makes it through and therefore wins them the pass. Although Izuku could have easily gained them the win by making his way there alone, he made the conscious decision to go back for his friend, not wanting to leave him behind.

This fight is one of the first major advances in the pair's relationship. It demonstrates their ability to work as a team, the true impact of Izuku's words on Katsuki, and ultimately foreshadows the possibility of them working as a hero duo in the future.

Season 3
In season three, Izuku pulls together a quick team after a harrowing fight with Muscular that left both of his arms shattered and furiously pursued the villain Mr. Compress, who was holding onto the compressed forms of both Tokoyami and Katsuki. They rescue Tokoyami but a portal opens up and pulls Katsuki in and Izuku desperately tries to reach him. He falls short with the portal closing and Katsuki's broken words being "Stay back, Deku." Deku falls to the ground and lets out a loud scream of anguish before passing out.

At the hospital, Izuku regains consciousness and begins to cry at how he couldn't reach him in time. Izuku and a few other classmates sneak out to go rescue Bakugou. Bakugou's kidnapping seemed to hit Izuku the hardest out of all the gathered students (except for Kirishima). While they are actually performing the rescue, Izuku seems to understand how Katsuki felt about the situation and was able to construct a plan that worked perfectly.

The episode "Deku Vs. Kacchan 2" revolves around Katsuki confronting Izuku about his quirk and how he got it from All Might. He then attempts to fight Izuku, who refused to resort to violence until he sees that he's "the only one who can accept Kacchan's feelings". During the beginning of battle, as they are fighting, Katsuki reveals to Izuku that he had been burdened by the thought of being the fall of All Might and that even if he wanted to forget about it, it would always come back to him - once again opening up to Izuku emotionally. After officially accepting Katsuki's challenge, Izuku takes a second to compliment Katsuki's strength: "''I know I'm stating the obvious, but you're really getting stronger". ''This triggers Katsuki to believe Izuku was scheming one of his tricks again and reveals that never knows what Izuku is thinking and that his attitude as if he was looking down on him and thinking he was better than him ever since they were kids was unbearable. Izuku realizes that this was how Katsuki had felt this entire time, and understands why he'd bullied him for so long.

Izuku counters Katsuki's feelings with his own, telling him that "to the same extent of all your unpleasant traits, your sheer amazingness at everything you do was so brilliant to me, it was blinding!" He then begins to get a little emotional and charges at Katsuki, "You, who had so many things that I never had... to me, you were an amazing, inspiring person, who was even closer to me than All Might!". And that was the reason he'd always chased after Katsuki. After a few hard kicks and punches, Izuku, in his mind, says "When my feeling of 'I need to win!' is stronger than my feeling of 'I need to rescue!', I'll carelessly run my mouth and say bad things." "And though that's supposed to be a part of me I rather dislike, in the end, in my mind, you're the image of 'victory'." This means that when Izuku's desire to win is stronger than his motive to save, he will begin to act more like Katsuki, because Katsuki is his "image of victory".

The two battle for the rest of the episode, ending in Katsuki's victory and All Might interfering afterwards. He tells Katsuki about the origins of One For All and his successor is Izuku and Katsuki promises to stay quiet. This becomes a secret the three of them share. All Might proclaims that the two have now become proper rivals after they've sorted out their feelings. Katsuki even gives advice to Izuku after he asks how his shoot style was, evidence of how the bond between them is slowly rekindling.

As children, Izuku and Katsuki are seen sharing an intense interest in Pro Heroes, especially in All Might himself, as they both see him to be a role-model in the way he both wins against villains and rescues those in need, all whilst doing it with a smile. These divided characteristics are what All Might tells Izuku and Katsuki are needed to be the ideal hero, and, if the two can "recognise each other and honestly raise each other up", then the pair can "become the best heroes, who both win and rescue."

All Might seems to greatly approve of Izuku and Katsuki's friendship, despite the way Katsuki outwardly expresses himself. In chapter 209, after Izuku tells Katsuki he'll catch up to him, All Might says, "that's a good friend you've got," in regards to Katsuki.

Season 4
The two don't share many interactions, however, the aftermath of their fight in season 3 shows through their character development. Katsuki, in particular, has changed significantly since his traumatizing experience at Kamino Ward.

Izuku is set to interview with Sir Night Eye in hopes of pursuing a work study under him. Mirio Togato asks him what kind of hero he wants to be, and Izuku explains that he wants to be a hero who always smiles, that he wants to be strong so nobody will worry about him, and he wants to be a hero who always wins and saves everyone, a call back to Deku Vs Kacchan. This time, Izuku validates Katsuki's admiration for All Might as someone who always wins. Something Katsuki was previously insecure about.

Before Eri's rescue, the class bombards Izuku and the other work study students with questions about their time at their hero agencies. Katsuki, as he sits directly in front of Izuku, scolds him about how he doesn't want to know about him moving ahead. Izuku is currently under a lot of distress, but Katsuki's harsh teasing seems to cheer him up slightly.

Much later in the season, Katsuki, who hasn't been around much this season, has his arc with Todoroki in order to earn their Provisional Hero License as he failed the exam in season 3. Katsuki must act as a caretaker for children in an exercise. One particularly stubborn kid, who holds the same mindset as Katsuki back in season 1, connects with Katsuki on a more personal level. While breaking through the kid's walls, Katsuki explains to him that if he only looks down at others, he won't be able to see his own weaknesses. While Katsuki had many influential people and events to teach him this lesson, the main person in his life that he learned this from was Izuku.

During the finale of season 4, Endeavor officially takes his place as the No. 1 hero and faces off against a high-end Nomu. Similar to All Might's battle with All For One being the end of his hero career, Endeavor's fight with this Nomu was the beginning of a new age of hero society. Without All Might, he must learn to define his status in his own way. The battle, for the students, however, is a reminder that hero society has to keep moving forward. The scene shows Izuku during his internal monologue explaining the future for him and his classmates, then shows Katsuki stoically staring at Endeavor's victory stance on the TV. This displaying the two's importance and how they will have to carry on what All Might had left behind one day, as they share their knowledge of One For All.

Two Heroes
In My Hero Academia: Two Heroes movie, although arguably non-canonical, provides one scene where Katsuki is shown to truly care about Izuku's wellbeing. At the end of the final fight, there is a scene where it becomes unclear as to whether Izuku will make it out alive - showing the class onlooking in fear, including Katsuki. Once Izuku is shown to be victorious, we are shown Katsuki smiling as he makes his appearance. Shoto notices this and smirks at him, to which Katsuki scoffs in response and looks away, walking off from the rest.

Manga
In chapter 210, Izuku unlocks the power of the Black Whip quirk as a result of his anger towards Monoma Neito's comment regarding Bakugou: "If you're [Bakugou's] friend, then tell me this. How can Bakugou-kun smile so confidently? Especially since he's the reason for the demise of the symbol of peace!". It is suggested later that this quirk manifests itself during an extreme emotional response, further reinforcing just how furious Izuku was at Monoma's attack on Bakugou.

During chapter 217, the two discuss One For All with All Might, with the pair now comfortable enough to sit on the same couch and have a normal conversation. Katsuki and Izuku are also seen training together in order to help Izuku master his newfound Black Whip quirk.

Katsuki and Izuku are seen sitting on the same couch again, discussing about One For All with All Might. Even All Might is shown smiling at them, proud of their development. Sero refers to them as "The house arrest boys" and Izuku later spends dinner with his classmates and thinks about how grateful he is of being here at U.A., All Might's guidance, and also specifically mentions having a normal-ish conversation with Katsuki. He was so in thought and says, "I'm so blessed" that he didn't realize Tokoyami was speaking to him.

In the Meta Liberation War arc, Shigaraki begins his search for Izuku in order to obtain One For All. Since Katsuki knows about OFA now, he rushes to Izuku's side saying, "because being a hero means protecting everyone." They both get so scared inside that they start seeing "the image of death" once again and Katsuki tries to lighten up the mood. When Izuku asks, "Kacchan, why are you following me?" Katsuki brushes him off by saying "I'll blow him to bits!" Izuku thanks him but Katsuki says outrightly, "Don't get the wrong idea! You think I'm here for you? Who do you think you are, some protagonist?...Since I'm the one who ended All Might..." Once Shigaraki actually started attacking them, Endeavor tells Katsuki to protect Izuku in which he does so without hesitation.

Katsuki helped Izuku train again, this time in what Izuku calls "Catch-a-Kacchan" as atonement, as shown in a flashback in chapter 284. Katsuki notices Izuku working hard and says, "That bastard doesn't know how special he is." All Might points out how Katsuki has his full trust in Izuku just like him. He also explained that he bullied Izuku because of his own feelings of weakness.

In chapter 285, Katsuki Bakugou: Rising, Izuku keeps getting extremely hurt during his battle with Shigaraki, even destroying his arm in the process. Katsuki is shown worrying and telling him to hold on. Katsuki thinks about all the moments they shared together before sacrificing himself for Izuku. He thought to himself, “At that moment, without thinking, my body simply moved on its own," paralleling how Izuku saved him in chapter 1. After pushing Izuku out of the way, Katsuki told him to not go play hero by himself. All For One proceeds to call this action useless, which triggered Izuku's new quirk, Danger Sense. He told the greatest evil himself, "Take that back!" Katsuki reflects on the situation later on. He thinks about how he had never felt the verge of death until he saw Izuku in danger, which also upgraded his quirk.

There’s a 2 day time skip from the time of the war in chapter 298, Katsuki regains consciousness. We see Mineta, Sato, Sero, and Hagakure visiting his room, with Mineta crying and hugging Katsuki in relief seeing that Katsuki is awake. Katsuki later asks about Izuku, Todoroki, Sensei, Senpai, and Endeavor to know if they are alright. A few panels later, Mineta and Sato are trying to hold Katsuki back, as he tries to find Izuku’s room after hearing that everybody regain consciousness except for Izuku and said “He's dead meat if he thinks he can die on me.”

Chapter 303 continues with Katsuki screaming Izuku’s name while coughing blood and was caught by his classmates in front of Izuku’s room. He said “Why are you asleep while I’m awake, huh!” While being carried along the corridor by Sato, Mineta, and Tsuyu. He later meets Best Jeanist and Hawks at the corridor. Hawks said hi, and Jeanist said “Great Explosion Murder God Dynamight, so you’re fine!” To which Katsuki responded “Does this look fine.”

In chapter 305, Bakugo is one of the people that he cares about.

Heroes Rising
My Hero Academia: Heroes Rising, which has ambiguous canonicity, expands upon the relationship between the two.

Katsuki spotted Izuku while he was training outside of Class 1-A's temporary hero agency. He gives Izuku his expected challenge of superiority through a fight once Izuku "makes One For All his own". Izuku claims that he knows Katsuki's way of thinking better than anyone else, referring to their shared childhood. They're then interrupted by Katsuma who claims that there's a "villain" attack.

They both rush to the scene only later to find out that the 'attack' was actually just the two siblings, Katsuma and Mahoro, testing the heroes with Mahoro's quirk to project a fake giant mantis. Izuku shows concern for Katsuki's well being once Katsuki sees through the rouse and willingly lets the 'villain' seemingly crush him. Katsuki proceeds to discipline the kids before Izuku intervenes and manages to hold him back. Katsuki nudges Izuku's face with his elbow, leading Deku to appear to be trying to kiss him, however, this was just an exaggerated face for slapstick. Izuku manages to tackle him before Katsuki lunges for the kids, and Izuku throws his hands over Katsuki's eyes to subdue him.

The next day, Katsuma goes to the temporary hero agency so that he can apologize to Izuku and Katsuki. Izuku who's on his way to the town accidentally sees Katsuma and approaches him. Katsuma confides in Izuku about wanting to be a hero. Izuku advises Katsuma that helping people, and wanting to be strong are equally important to become a hero. This was referencing Katsuki's insecurity of looking up to All Might in the 'wrong way', as Katsuki wants to be the strongest in order to win. Katsuki overhears all of this from nearby and holds a silent moment of thoughtfulness over Izuku's words of consideration.

After the villains attack Nabou Island, Izuku boldly grabs a phone out of Katsuki's hand in the middle of his call.

During Izuku's first fight with Nine, he's badly injured while trying to help Mahoro and Katsuma escape. After Mahoro signals that Izuku is in trouble by using her quirk, Katsuki arrives almost instantaneously to help Izuku who's relieved to see him comes to their aid. They step up against Nine, but lose and have to be saved by their friends. After they recover, thanks to Katsuma's quirk, then regroup with class 1-A. Izuku convinces them to fight back to save the island, formulating a plan to stop Nine and his crew, which Katsuki willing goes along with.

The two face off against Nine once again. Katsuki willingly accepts Izuku's partnership in the fight, even locking hands for a combined super move called "Explode-A-Pult". At one point in the middle of the fight, Izuku loses his focus and needs to be saved by Katsuki from Nine's attack.

As the battle continues, and the two aren't able to defeat Nine, Izuku tells Katsuki that there's only one way to defeat him. Izuku reaches his hand out to Katsuki, which he takes with some hesitation, concern, and frustration. Izuku transfers One For All to Katsuki in hopes to be able to fight off Nine with the embers. The two enact a "Double Detroit Smash" into the sky creating a colorful cyclone that punched a hole through Nine's storm clouds. As the two prepare to face Nine, Katsuki shows concern for Izuku's dreams of being a hero, telling him that this would be the end and he'd be quirkless, again. Izuku shows no concern for this, telling him "It's okay if it's you," expressing Katsuki's worthiness to hold One For All and Izuku's trust in him. The two charge Nine, the power showing them becoming one and delivering a final combo attack that finally able to defeat the villain.

After the fight, Izuku shows his concern for Katsuki, telling All Might that he made him do something "crazy". All Might reaffirms Izuku with an understanding of the two's relationship. By the will of the successor, One For All is returned to Izuku. Katsuki wakes up with no memory of the transfer. He sits in the recoverry center in annoyance due to Recovery Girl giving him her healing kiss, which Izuku laughs at with Katsuma. Both Izuku and Katsuki are shown dropping off Mahoro and Katsuma to see their father, sharing some closure before returning to the temporary hero agency. As Class 1-A departs from Nabou Island, Izuku joins Katsuki on his isolated part of the ship. Katsuki asks Izuku whether it's okay or not leaving the island without saying goodbye to the siblings. Izuku explains that he believed to have said all that he needed to say. Later on, the siblings are shown chasing the ship. They thank the heroes for saving the village as well as Katsuma promises that he'll become stronger so that he can become a hero like Izuku and Katsuki. Hearing this, Izuku and Katsuki smile as the two wave goodbye to Katsuma and Mahoro. Izuku encouraging him by saying "You can be a hero!"

Fanon
In the Eastern side of the fan base, BakuDeku is arguably the most popular ship among fans due to their complex relationship and how their frequent interactions explore the classic rivals and childhood friends trope. Their dynamic is about growth and forgiveness which makes BakuDeku stand out from the other ships in MHA.

In the Western community, the pairing is still widely appreciated, however some believe the two will have an abusive relationship due to Katsuki's personal issues surrounding his inability to express himself without using anger and Izuku's past inability to defend himself. The main reason is because Katsuki told Izuku to take a swan dive off the roof in Season 1. Despite this opinion, the pair is undoubtably gradually repairing their relationship as the story continues, with Katsuki learning to accept Izuku for who he is and being a constant positive presence during the hardships they face.

On AO3, BakuDeku is the most written ship for both Katsuki and Izuku and in the My Hero Academia tag. It's the 7th most popular ship in 2020. They also placed 25th overall.

Fandom
FAN FICTION
 * Izuku/Katsuki tag on FanFiction.net
 * Izuku/Katsuki tag on FanFiction.net

TUMBLR

Trivia

 * The term 'Wonder Duo' comes from a mistranslation where All Might calls Izuku and Katsuki the same name before they team up to fight him in chapter 61. It has since become a popular ship name.
 * There are several instances where the pair have been referenced to as 'stars', mainly in fanon. On April 20th 2018, a fan of the pair purchased an acre of the moon and named it after Bakugou on his birthday as a gift for Horikoshi. Not long after, a star was also named after Bakugou, along with another named after Izuku. In chapter 106 of the manga, a rough translation has the two described as the 'Twin Stars of Class 1-A'.
 * On July 20th 2018, a Twitter announcement on the My Hero Academia: Two Heroes account asked all My Hero Academia fans to vote for their favorite pair in the show, and the duo that wins would get their character colors shone on Kyoto Tower for promotion to the release of the movie. The poll ended on August 1st, crowning BakuDeku first place with over a whopping one million votes. Izuku's vibrant green and Bakugou's fiery orange lit up Japan's evening sky, proudly glowing in unison.
 * A Chinese fanmade visual novel was developed by creator Ego and artist Ten featuring a plot on Izuku and Katsuki getting together. There are three endings: Normal, Good, and True. Warning: The true ending features explicit content. There are both English and Chinese versions of this game.
 * In a set of official licensed poker cards for the series. Respectively, Izuku represents the Ace of Hearts while Bakugou represents the Ace of Diamonds. But together, they represent the King of Hearts.
 * The pair have an instrumental song composed after them titled ' Katsuki and Izuku ', which contains a mix of their signature tracks ' You Say Run ' and 'Bombing King '.
 * Season 2's second ending, Datte Atashi no Hero ('Because You're My Hero' in English), was written by LiSA, who confirmed that the song's lyrics are written to represent Izuku‘s genuine feelings towards Katsuki.
 * Some of the song's lines translate to "you give me courage", "when I see those eyes, I can start running too!" and "I want to try and look at the goal that's only yours and mine." The "when I see those eyes" line plays as the ending shows Izuku and Katsuki looking at each other before teaming up to fight, originally against working together; metaphorical for their relationship growing in the series.
 * BakuDeku has been featured on Fandometrics' most reblogged ships list several times; it was the seventh most reblogged ship the week ending July 20th, 2020.
 * In the chapter cover page of Chapter 214 featuring the continued medieval spinoff, Katsuki and Izuku are wielding two halves of one sword.
 * Horikoshi once drew official art to celebrate the new movie, which depicts Katsuki as Godzilla and Izuku as Mothra. They are known as the King and Queen of kaijū in the popular Godzilla Franchise.
 * In honor of the second My Hero Academia movie's premiere, they have a hallway dedicated to their relationship throughout the series.
 * According to Masadora Charts, BakuDeku placed the 2nd spot (only after SasuSaku) as the Best-Selling anime couple of the decade on the site ('18-'19). DekuBaku also claimed the 7th spot, making it the most popular BNHA ship in China.


 * Horikoshi's assistant, Noguchi, often draws Katsuki and Izuku together and refers the ship as Decchan. Their twitter is @nstime23.
 * In a panel that featured the Izuku's and Katsuki's English voice actors, Justin Briner and Clifford Chapin, both of them were joking about how they read some “Dekugo” fanfics for research.
 * On twitter, the BakuDeku stans went crazy after they saw that John Cena followed various accounts who openly ship BakuDeku.

Variations

 * BakuDekuChako refers to the ship between Bakugou, Midoriya and Ochako Uraraka
 * TodoBakuDeku refers to the ship between Shoto Todoroki, Midoriya, and Bakugou
 * TodoBakuKiriDeku refers to the friendship ship between Shoto Todoroki, Midoriya, Bakugou, and Eijiro Kirishima

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