Dazatsu

"Dazai always wanted to die. Nobody knew why. All I know is that I'd never be able to forgive myself if I let him go like this."

- Atsushi determined to save Dazai from death in 55 Minutes.

Dazatsu is the slash ship between Osamu Dazai and Atsushi Nakajima from the Bungou Stray Dogs fandom.

Canon
Dazai was the first person to help Atsushi when he was kicked out from the orphanage. Atsushi saved him from his drowning attempt, showing skeptism and confusion towards Dazai's behavior. The latter takes a liking to Atsushi, giving him food (with Kunikida paying) and bringing him to the warehouse to reveal that Atsushi was the man-eating tiger all along. The next day after the events, Dazai offers a position among the Armed Detective Agency. Dazai was the person who recommended Atsushi to the Agency's boss.

It is shown throughout the series that Dazai cares a lot for Atsushi as a friend and mentor. For example, after the incident with Q, Dazai calmed Atsushi down while the latter was falling into a spiral of self-doubt despite doing it forcefully. He lets himself get kidnapped by the Port Mafia in order to learn who placed the 7 billion Yen bounty on Atsushi's head. Dazai has repeatedly helped Atsushi, being there to protect and comfort him. He is always wanting the best for Atsushi. Dazai has a tendency to mess with Atsushi, taking advantage of Atsushi's naivete to play jokes on him.

Atsushi has shown he cares a lot for Dazai and looks up to him a great deal. As the series progresses, when he finds himself in a difficult situation, Atsushi thinks "What would Dazai-san do?", instead of breaking down as he would have earlier in the story. During the Decay of Angels Arc, despite being imprisoned, Dazai appears to Atsushi, offering him encouragement and advice even when he is not physically by his side. Atsushi tries to help Dazai when he gets himself into trouble, like during the second episode when Dazai gets stuck in an oil drum as a method of suicide.

When Dazai is acting out his plans with Fyodor, he says to himself "I hope Atsushi-kun and the others are okay", notably emphasizing Atsushi was the first person he thought of and worried about. After the calamity of the film is over and Dazai is no longer acting with the villains, he finds Atsushi and attempts to explain why he was 'siding' with the villains. Before even hearing what he has to say, Atsushi remarks that Dazai saved the city. They share an exchange similar to that of the beginning of the movie, where Dazai asks if he seems like such a good person to attempt to save the city and Atsushi innocently responds with the same words as last time, making Dazai smile.

Whenever Dazai appears to be doubting himself and whether he is truly a good person, Atsushi is there to remind him in a pure and honest way that he is. On the other hand, when Atsushi is down on his luck or recalling his past, Dazai acts as a voice of reason and a motivator for Atsushi to keep persevering.

In the anime's first ending, 'Namae Wo Yobu Yo' by Luck Life, the two are also featured together. While laying down, Atsushi attempts to reach out for Dazai's hand. Dazai later reciprocates this by placing his hand on Atsushi's head.

Port Mafia Arc
Atsushi is starving after being kicked out of the orphanage and plans to rob someone for money. As he fails in multiple attempts, he then spots a man floating in the river drowning. Atsushi remains silent and nervous, not knowing what to do but eventually shaking off his doubts and jumping straight into the river to save the man. This man is revealed to Dazai, and he wakes up saying, "I lived. Tch." Atsushi responds, startled, "'Damn'?! Did this guy just go 'tch' at me?!" weirded out by Dazai. Dazai slowly gets up and asks if Atsushi was the one who interrupted his drowning, and Atsushi is confused. Dazai, finding this amusing, responds saying he was attempting to commit suicide. Atsushi is shocked and Dazai explains with a sigh his goal was to commit a clean suicide, and since he troubled Atsushi, wanted to get some food for him. After some bantering, Kunikida appears and starts snapping at Dazai for ruining his schedule as Atsushi watches in confusion. Dazai asks Atsushi's name and he responds; after Dazai asks Atsushi what he'd like to eat, he responds with Chazuke and Dazai heartily laughs announcing how a boy on the brink of starvation is asking for Chazuke. He says he'll serve Atsushi 40 bowls of that, and Atsushi inquires Dazai's name. Dazai responds, "Yeah. That's my name. Dazai. Dazai Osamu."

Atsushi stuffs himself with chazuke as Dazai and Kunikida bicker back and forth. After discovering they're apart of a detective agency, Atsushi wonders how these two are actual government agents. Eventually after Kunikida queries Atsushi on the tiger as the latter attempts to run, Dazai bribes Atsushi with a sum of money to be bait at a warehouse for a tiger. Later, Atsushi is shocked how Dazai cold read in the dark. Once Dazai reveals that Atsushi is the moonlight beast himself, he easily dodges the tiger's attacks and neutralizes Atsushi's ability. A comical scene plays out as Atsushi falls unconscious against Dazai's chest, and Dazai pushes him away stating "Sorry, I'm not into hugging men." (Or "If you're flirting, I'm not interested.")

After Dazai announces Atsushi will be joining the agency, the next day Atsushi is woken up by a call from Dazai to his surprise, the latter calling for help. Atsushi quickly leaves his room only to be confuddled by Dazai sitting in an oil drum attempting to commit suicide. He goes on a monologue on how this turned out to be a torture method, and confused, Atsushi knocks Dazai forward to help him out. Afterwards, Atsushi sadly tells Dazai he's not fit for the job at the agency. Dazai remains expressionless during this but then announces he has an alternative job for Atsushi, and the latter thanks Dazai and the two set off. Dazai brags how he's the most loved and trusted member of the agency, and he's interrupted by Kunikida stomping over to him and reading out a list of complaints filed to Dazai. Atsushi watches the two interact with confusion, but afterwards Kunikida explains there's a terrorist holed up with a bomb back at the agency. Atsushi gets dragged along, and the latter is hesitant and scared watching the terrorist (who is Jun'ichiro), and Atsushi watches as Kunikida and Dazai play rock-paper-scissors to determine who distracts the bomber. Again, Atsushi is weirded out by the agency's methods. Dazai convinces Atsushi to properly distract the bomber, presumably teasing him despite giving him encouragement.

When Atsushi uses himself as a human shield to stop the bomb, Dazai yells out "IDIOT!", one of the only times he showed genuine anger and emotion throughout the series. Why Dazai reacted this way while knowing the bomb was a dud is unknown, however it can be presumed Dazai didn't want Atsushi to willingly squander his life for others.

Dead Apple
At the beginning of the movie, the two share a moment at Yokohama's graveyard, where Dazai melancholically confides in Atsushi about Oda Sakunosuke, his late friend, and confesses that without him, he may have stayed in the mafia, killing people. Dazai is seldom emotionally vulnerable around others, making this moment stand out. At the end of the scene, he plays off his solemn attitude with humor, hinting that he doesn't want Atsushi to lose his faith in Dazai due to his gruesome past. At first, Dazai denies being there to visit Oda and asks if it looks like he is visiting a grave, to which Atsushi replies that it does, surprising Dazai.

Upon hearing Dazai is at the enemy's headquarters, Atsushi assumes he has been taken hostage and wants desperately to save him. And, even when learning the truth that Dazai had not been kidnapped but has, in fact, been assisting the enemy, Atsushi is reluctant to believe it. When Akutagawa proclaims that he will kill Dazai, Atsushi levels a gun to his head, saying "I won't let you kill Dazai-san."

BSD Wan!
'Bungo Stray Dogs Wan!', the series' spin-off featuring the characters in chibi forms, has quite a few notable Dazatsu moments in it as well. At the end of the short 'The Armed Detective Agency Beats the Heat', adapted in episode 10, Dazai makes a (not out of character) comment about wanting to die as beautifully as a firework. Atsushi, concerned, tells Dazai he'd rather he didn't die, to which he receives no response. Usually, in the spin-off's ending, Atsushi can be seen skipping to the ending theme with a smile on his face. However, in this episode, he simply sits by the riverbank with a blank expression, before turning his head to the left. He is likely waiting to see Dazai floating down the river, a reference to how they met in the very first episode of the main series. A short scene then plays in the middle of the ending where, Atsushi, visibly distressed and trembling, tells Dazai not to say things like that, even if he is joking. Again, he receives no response and Dazai continues to watch the fireworks. As the ending goes back to Atsushi by the riverbank, the sky is pitch black and Atsushi's head is in his arms. Knowing that his mentor will not show up, he gets up to leave. This can be interpreted as Atsushi realizing for the first time that, someday, Dazai may actually end up killing himself and, never having had a mentor or place to belong before meeting Dazai, Atsushi clearly feels somewhat attached to him.

We see Dazai acting his regular cheerful self. He messes with Atsushi on multiple occasions, like in the short 'What's Inside the Locker?' in episode 1, when he convinces Atsushi to slack off from work and snoop around the agency members' lockers as part of their 'cleaning duties', 'Miscellany on Shrimp Tails' in episode 9, in which he tries to convince Atsushi that shrimp can be regrown if buried in soil, similar to a tree branch or pea sprouts, and 'Me Drawing You Drawing Me' during the same episode, where the two are drawing one another and Dazai presents his picture to Atsushi, having drawn a menacing looking shadow behind him claiming he is 'having a hard time drawing the person behind [Atsushi]', despite there being nothing there. Before they share their drawings, Atsushi is also notably excited at the prospect of Dazai struggling with something, reinforcing his view that Dazai is a person to be held in high esteem. The last significant Dazatsu moment of the first season occurs during the 12th episode, in the last short, titled 'Nakajima Atsushi's Plan'. Atsushi, frustrated that he's always being pranked and confused by Dazai, decides he wants to see Dazai looking equally as surprised. He enlists the help of the other agency members, to no avail, and eventually decides to go about it his own way. He meets Dazai at the door of the Detective Agency building and presents him with a bouquet of flowers, while thanking him for everything he has done. Dazai, so shocked by his gesture of kindness, passes out.

55 Minutes
Atsushi notices something amiss about the case they have been assigned on the island they're travelled to. When the Shell is activated and starts to destory the entire world, Atsushi heads back in time by 55 minutes with the help of H.G. Wells. He's warned by the former to give no insight of the future events to any of Atsushi's friend, but Atsushi disobeys the warning and tells Kunikida and Dazai everything that had happened. Atsushi is forced to infiltrate the group of thieves and Dazai suggests the nickname Matasaburou of the Wind for Atsushi to use as an alias. It is revealed that he chooses this name purely for his own amusement, messing with Atsushi yet again. There are also several sentimental moments between them during the novel. In a memory, Atsushi, while following along behind Dazai, comes to the realization that Dazai is not completely flawless and has many human faults, contrary to what he once believed. After being advised by Kunikida, Atsushi is sure Dazai will figure out exactly what to do.

Towards the end of the light novel, Dazai ends up in mortal danger due to a stab wound from Jules Gabirel Verne (Gab) and Atsushi is tasked with saving him. In an effort to reach Yosano, who can save Dazai, Atsushi is in peril alongside Akutagawa, as Dazai is about to die from blood loss. Akutagawa stabs Atsushi in the throat and as the latter blacks out, he recalls a conversation he had with Dazai where he asked Dazai, "Why do you want to kill yourself?" Dazai pauses in the memory and responds but Atsushi can't remember what he says - then, an unusually aggressive side of Atsushi turning into his true beast form activates, spurred on by the desire to save Dazai. This violent side is even noted by Gab. Atsushi is asked by Gab if he wishes to save Dazai, to which he responds ' ''Of course. No matter what it costs.'''

Once the events wrap up, Atsushi is greatly relieved to see Dazai alive due to Yosano's ability, and Dazai immediately teases Atsushi over his relationship with Kyouka.

Fanon
Dazatsu is the fourth most written ship within the fandom on AO3; Dazai's second most written and Atsushi's second as well. It also has a fair amount of fan art. Though it's often overshadowed by more popular ships such as Soukoku and Shin Soukoku. Fans also view the ship as a mentor-student ship. Despite this, Dazatsu is still a very popular ship within its fandom.

Fandom
FAN FICTION
 * Atsushi/Dazushi tag on FanFiction.Net
 * Atsushi/Dazushi tag on FanFiction.Net

INSTAGRAM 
 * @deviant.dazushi account related to Dazushi ship on Instagram.
 * @mrsdazushi account related mostly to Dazushi ship on Instagram.
 * @jinko.tiger account related to Bungou Stray Dogs (but there's a lot of Dazushi) on Instagram.
 * @bsd.shipping.hell account related to BSD ships (there's a lot of Dazushi) on Instagram.

YOUTUBE
 * Ocehamada have a few Dazatsu related (awesome) edits on Youtube.

Trivia

 * In a lot of moments when Dazai and Atsushi are together, we can see the sunset in the background - one of the backgrounds that are described as the most romantic scenery.
 * They have a duality card together in the mobile game 'Bungou Stray Dogs: Tales of the Lost', as well as several cards with subskills that activate when a card of the other is on the team.