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Act 1: Hero Work Recommendation Project
Every student from Class 1-A has been assigned to the Hero Work Recommendation Project. A month ago, Shota Aizawa informed Class 1-A of UA High School that they will participate in the program sponsored by the Hero Public Safety Commission to help with their training after everyone obtained their provisional licenses. They were sent to Nabu Island to perform duties as heroes acting like their own "UA Agency" without the aid of any teacher. Their work would involve mostly minor deeds with the island's relatively low crime rate. The Pro Hero who used to protect the Island retired and now the UA Agency takes requests and calls from all the civilians.
Ochako gets a call from a little girl who lost her brother somewhere on the island, and calls across the room and asks if anyone can help her to find the lost kid. Izuku and Kyōka volunteer. The three search the island and find Katsuma at a nearby park. His older sister, Mahoro suddenly appears and scolds Izuku for taking so long to find them, revealing that she was timing Izuku and the others on their arrival to their location.
She angrily scowls at Izuku because he took about an hour late to locate her brother. Izuku felt embarrassed and ashamed before Mahoro disapproves of him for being a hero, as she doesn't appear to be fond of heroes, and walks away with her brother. Ochako and Kyōka are confused by the exchange, but Izuku doesn't mind being scolded by the child. He is just happy the little boy is with his sister.
Elsewhere, Mahoro gets Katsuma and herself some ice cream while making rude comments about UA High's students and their inability to respond to danger despite the island's low crime rate. Katsuma doesn't seem as bothered as his sister because Izuku was kind to him, so Mahoro formulates a plan to make her brother change his mind about the heroes.
Later on the night, Izuku is practicing his kicks to keep training on the One For All. He thinks about his Quirk and how he can train himself to be able to use this power that All Might has given him. Coming back from his patrol, Katsuki finds Izuku training and tells him to hurry and master his Quirk. They have an exchange over who will be the No. 1 Hero before it's interrupted by Katsuma. The young boy tells them a villain has appeared. Deku is surprised by the presence of a villain before Katsuki pushes him aside, demanding Katsuma to explain himself better.
Katsuki rushes over to where Katsuma said the villain is located, carrying the little kid and being followed by Izuku. Katsuma tells him he saw the villain at the ancient castle ruins located in Mount Shiroyama, on a smaller island next to Nabu. Katsuki arrives on scene first to confront the villain: a giant praying mantis wreaking havoc on the side of the hill. Katsuki uses Stun Grenade to blind it, but he notices something wrong and stops attacking.
Izuku arrives shortly afterward and sees the praying mantis attacking Katsuki, but it phases through him. Katsuki generates a huge explosion that makes Mahoro fall from her hiding place. The giant mantis disappears, confirming Katsuki's suspicions that the monster was fake because there was no shadow beneath it. The creature was created by Mahoro's Quirk: Hologram.
Katsuki is furious as he shouts to the girl if she's trying to make fun of him. He tells her that he's aiming to be Number 1 and doesn't need stupid kids to play pranks on him. Katsuki scolds Mahoro and Katsuma with an increasingly angry face for having faked a villain attack, forcing Izuku to restrain him for fear that he will hurt the kids. Katsuma and Mahoro scurry off while Katsuki struggles to get Izuku off him.
The kids end up in a sugar cane field as they look at the stars. Mahoro complains about Katsuki, saying that even though he wants to be a hero he seems more like a villain, reinforcing her dislike for heroes because they're all talk. Katsuma tells him that despite that those two boys went to help them. Mahoro is aware that her little brother is fond of heroes and wants to be one, but she says their father is better than any hero.
The next day, the class resumes to their daily schedule hero work. Izuku comes across Katsuma again, who apologizes for his sister's prank last night. Katsuki also listens to Katsuma's apology as he is outside standing on the veranda. He listens to Katsuma explaining that Mahoro was trying to prove that the heroes wouldn't come help but they did just like Katsuma believed.
Deku notes that Katsuma has an Edgeshot pin on his bag, and asks him if he likes heroes. Katsuma says that he really admires Heroes and wants to be one even though his Quirk isn't suited for combat. However, his sister dislikes heroes and wants to discourage him from ever becoming one. Izuku realizes that Mahoro doesn't quite hate heroes, she just wants to stop Katsuma from thinking of becoming one because she was afraid that hero work is dangerous, which reminds him of how his mother, Inko, was worried about his well-being.
Izuku assures Katsuma that anyone can be a hero as long as they focus on putting in their effort. After Katsuma leaves, one of the residents tells Izuku that Katsuma and Mahoro live alone with their father on the island. Their mother passed away from a particular illness when they were very young, and the village watches after them while their father is away working. That's why Mahoro is very protective of her brother. Katsuki overhears everything from the balcony.
Act 2: Nine's Invasion
By sunset, Katsuma meets back with Mahoro at the same park where he met Izuku and is about to tell his sister about becoming a hero when Nine and his villains hijack a ferry and crash into the Nabu Island harbor. Residents flee as the villains arrived. Once the villains have landed on the island, the villains begin their assault.
Nine instructs his allies to do whatever they need to do in order to create distractions while he hunts down the two kids. Slice uses her Quirk to destroy all of the ships at the harbor while Nine and the rest of the villains continue their attack. Terrified, Katsuma and Mahoro attempt to contact Class 1-A headquarters, but Katsuki answers the phone. He doesn't believe her at first but Izuku hears the exchange and takes the phone. Just before Izuku can answer back, the phone service is cut off after Chimera destroyed the communication towers, rendering all connections to the outside world severed.
Once the connection is cut off, the villains continue with their invasion. Meanwhile the Class 1-A are fighting, Katsuma and Mahoro run away from the scene of the fighting and attempt to get back home, but they run into Nine, who destroys their home. The villain uses his Quirk to scan the little kids and finds out that Katsuma has the exact Cell Activation Quirk he needed. Before Nine can steal Katsuma's Quirk, Izuku arrives and rescues the kids, using his Quirk to escape through a forest area and get the kids to safety.
Izuku fights Nine using his Quirk at 8%, but Nine uses his Air Wall Quirk to create a barrier that is made of highly compressed air to shield himself. Izuku retreats after Nine uses his Bullet Laser Quirk to shoot purple laser beams over to Izuku. The hero realizes that Nine has the same Quirk as All For One, and attacks using Delaware Smash Air Force, but Nine uses the Air Wall Quirk to shield himself and retaliate by using it to push a gust of wind directly at Izuku. He then activates One For All: Full Cowl at 20% and uses St. Louis Smash, but despite increasing his power, Izuku is still outmatched by Nine.
Using his Scanning Quirk, Nine realizes that Izuku has an interesting Quirk and attempts to use his All For One Quirk to steal it. While Nine tries to steal Izuku's Quirk, something stopped the process, leaving Izuku temporarily immobile. Nine is surprised that he can't steal Izuku's Quirk, and assumes, due to him also possessing multiple Quirks, it is because he has no room for it. Disappointed for not being able to snatch his Quirk, Nine blasts a defenseless Izuku, slamming him hard against a nearby hill.
Mahoro and Katsuma try to help Izuku, but he orders them to flee. Nine proceeds to shoot a purple laser at Izuku's chest, wounding him. Frightened, Mahoro uses her Quirk to project a cartoony version of the wounded Izuku to notify everyone. Before Nine can dispose of Izuku, Katsuki arrives and engages in combat with Nine, but even he, alone, is no match for Nine and his multiple Quirks. Katsuki manages to outsmart the villain and is about to attack him up close when Nine activates his Hydra Quirk and pins down him.
Izuku manages to recover and attacks Nine. As Izuku is close to landing a blow at Nine, the villain uses his original Weather Manipulation Quirk to summon a massive lightning strike to zap Izuku and Katsuki, severely injuring them in the process, while at the same time, causing a major blackout throughout Nabu Island. With Izuku and Katsuki down, Nine goes after the children, but then, he suffers from his cell degeneration disease and is unable to continue fighting.
Slice arrives to help Nine and attempts to take Katsuma before Koda uses his Anivoice Quirk to summon a swarm of crows to blind the villains while Mezo, Tsuyu, and Ochako rescue the wounded Izuku and Katsuki and the children. Nine orders Slice to chase them but she assures him that they cannot leave the island and what they must do now is withdraw so that he can recover. With the kids gone and Nine in pain from his illness, Slice fires a flare gun to call all their allies to retreat.
Act 3: Preparations for the Last Stand
Later at night, Class 1-A regroups and holds out in a factory with all the civilians that they've managed to save and providing humanitarian aid to the local residents. Mummy was captured, locked up, and chained inside the machine room, but he refuses to talk to any of them after they questioned the villain. Momo and Denki are currently working on maintaining essential supplies.
Ochako goes into the room where other civilians are being healed by medical staff from the hospital clinic with healing Quirks. Izuku and Katsuki are both unconscious and the Doctors can only use their Quirks to close their wounds, but they cannot treat them any further because they've suffered so much damage that they need to be sent to a hospital in the mainland. Mahoro and Katsuma then come into the room and they say that he can help using his Cell Activation Quirk to heal both Izuku and Katsuki. The doctors appreciate his help, and invite him to heal both heroes. Katsuma continues trying his hardest to heal Deku and Katsuki with his Quirk, to the point where he almost passes out. His sister asks him to get some rest but he refuses to give up and continues using his Cell Activation Quirk, until finally both Izuku and Katsuki start waking up
In another room, Class 1-A holds a meeting to discuss how to deal with the major threat from Nine and the rest of the villains. Momo created a drone to send an SOS out to the mainland but won't arrive for six more hours. They are trying to figure out what the villains are after when Katsuma and Mahoro enter the room, and the little boy reveals that he is the target for the villains, since Nine wants to steal his Quirk.
Some students suggest helping the boy escape to thwart the villain's plans, but Shoto advises against it as they could kill the inhabitants of the island in retaliation. Katsuma then offers to surrender himself to Nine to save everyone, but Izuku appears, having fully recovered after Katsuma healed him, and dissuades the boy of his idea by telling him he has an amazing Quirk that he should never give up. Katsuki also enters the room fully healed and tells everyone that the only thing to do is to crush the villains.
Inspired by Izuku and Katsuki’s words, the class thinks back on all of the hard work they've done for the people and are now determined to do the same as Izuku and Katsuki. The whole class unanimously agrees to fight the villains and protect everyone on the island.
Izuku devises a plan of action for the class: by relocating all the civilians to Mount Shiroyama in the smaller island where the ancient castle is located, it can hold all of the residents in the large cave safely. This way, the villains only have one route to get to Katsuma and everyone has an escape route if needed. The heroes will engage the villains using the terrain to their advantage and spit the villains apart. Mashirao, Kyōka, and Mezo will personally guard Katsuma and Mahoro while the civilians are holding out inside the cave protected by Koji, Rikido, and Toru.
Shoto questions about how the class is going to deal with Nine and his multiple Quirks. Izuku noted that Nine can only use his Quirk for a limited time due to the illness he is suffering, so the plan is to have everyone attack in waves to make sure the villain uses his Quirk all the time until he has reached his limit and hold out until reinforcements from the mainland arrive.
The next morning, after recovering from his illness, Nine, Slice, and Chimera arrive at the entrance to the island after Slice scouted them on the ruins of the ancient castle. The villains make their way to Mount Shiroyama, determined to take Katsuma no matter the cost.
Act 4: Rising
After Minoru, Ochako and Hanta 'fails' to defeat the villain, Izuku and Katsuki engages the villain, but they aren't strong enough to take down the villain as Nine uses his Air Wall and Bullet Laser Quirks to defend and attack at the same time. Hanta attempts to help out, but he is defeated after Nine uses his Bullet Laser Quirk to blast him. Ochako tries to make Nine floats but she gets knocked out by his Hydra Quirk. Izuku and Katsuki fire back against the Hydra Quirk with a combination of Delaware Air Force and AP Shot, but the Quirk is too much and takes them both down.
As the villain's about to defeat Izuku and Katsuki, Nine has reached his limit and starts to reel in pain from his illness. Izuku and Katsuki seize the opportunity, but Nine activates his life-support to take a heavy dose of empowering drug and goes beyond his limit, summoning a massive lightning strike that seemingly vaporized Izuku and Katsuki.
The situation for Class 1-A is growing dire as Nine was proven to be too powerful for all of them. Mashirao, Mezo, and Kyōka flee with Katsuma and Mahoro to the escape route in the caves. Mezo takes the kids away while Mashirao and Kyōka ambush the villain first to hold him back but they are smashed by the Hydra Quirk. Nine later catches up to Mezo and attacks him using his Bullet Lasers as Mezo protects the kids. Mashirao and Kyōka catch up to attack Nine with Mezo tackling with his Dupli-Arms Quirk, but the villain blasts all three of them away, defeating them.
Nine holds Mahoro hostage to demand Katsuma to surrender his Quirk or he will kill his sister. Before Nine can steal his Quirk, Izuku and Katsuki enter the fray to save Katsuma and Mahoro, revealing that they survived the lightning strike using Denki as a lightning rod to absorb the lightning.
Izuku and Katsuki gain the advantage after Nine is reaching his limits of using his multiple Quirks and overwhelms him with a combination of Detroit Smash and Explosion. On the verge of defeat, Nine uses the entire empowering drug in his life-support system which amplifies his Weather Manipulation Quirk to the maximum and summons a massive fire tornado and lightning storm and begins to destroy everything on the island.
Izuku boosts his Quirk to reach 100% and uses Detroit Smash while Katsuki uses Howitzer Impact, but the two aren't strong enough to stop Nine and gets obliterated by the Weather Manipulation Quirk. Mezo manages to regain consciousness and uses his body to shield Katsuma and Mahoro from falling debris as the firestorm causes a cave-in, trapping Koji, Rikido, and Toru along with the civilians in the cave. Izuku and Katsuki manage to survive, but they are severely wounded. Nine proceeds to decimate them with his Bullet Laser and uses his Hydra to start crushing them to death.
With the entire class down and wounded, Izuku makes the desperate gamble; he transfers One For All to Katsuki, breaking the grip from Nine. Infuriated, Nine attempts to kill them by summoning another massive storm on the island, destroying much of the island's infrastructure. Katsuki boosts up to reach One For All: Full Cowl - 100% and together with Izuku, they use Detroit Smash to stop the tornado.
Nine is just shocked by what he just witnessed, but he still refuses to give up on fulfilling his dreams, and engages Izuku and Katsuki in a intense combat, releasing all his Quirks at their maximum power. After a lengthy fight, Izuku and Katsuki finally manage to defeat Nine once and for all using the Explosion Quirk combined with St. Louis Smash at 100%, effectively ending the threat, but the ember left by One For All sparks out, leaving Izuku permanently Quirkless once again. Both heroes pass out from their injuries and exhaustion. As Izuku loses consciousness, he thanks One For All for everything as its last embers are extinguished inside him.
Izuku has a conversation with Katsuki, who suffered amnesia where he doesn't remember using One For All. Katsuma and Mahoro, who are reunited with their father, say their good-byes to Class 1-A for protecting them and saving the island. Katsuma promises to get stronger and Izuku tells him that he can become a hero and he will be waiting for him at UA while Katsuki smirks watching them.
The family ship between them is very popular among BakuDeku shippers since the movie Heroes: Rising released. The headcanon of Katsuki and Izuku being their parents is one of the headcanon that the shippers like. This family ship is pretty popular, but not as popular as Aizawa Family due to not so many people remembers Mahoro & Katsuma/even watch the movie. BakuDeku is also a ship that many people dislike/hates, so it's not very popular. There's only 8 works of them in AO3 for now.
- Katsuma's relationship with Mahoro on My Hero Academia Wiki
- Katsuma's relationship with Izuku on My Hero Academia Wiki
- Katsuma's relationship with Katsuki on My Hero Academia Wiki
- Mahoro's relationship with Katsuki on My Hero Academia Wiki
- Mahoro's relationship with Katsuma on My Hero Academia Wiki
- Mahoro's relationship with Izuku on My Hero Academia Wiki
- Katsuki's relationship with Izuku on My Hero Academia Wiki
- Izuku's relationship with Katsuki on My Hero Academia Wiki
- BakuDeku refers to the ship between the Katsuki and Izuku
- KatsuTsuma refers to the ship between Katsuki Bakugou and Katsuma
- KatsuHoro refers to the ship between Katsuki and Mahoro
- IzuTsuma refers to the ship between Izuku and Katsuma
- IzuHoro refers to the ship between Izuku and Mahoro
- Shimano Siblings refers to the ship between the Mahoro and Katsuma