"What's better than being alive?"
|Also Known As||Man-Tiger / Jinko|
White Reaper (in BEAST - White Akutagawa, Black Atsushi -)
|Birthday||May 5 (Taurus)|
|Height||170 cm (5'6")|
|Likes||Chazuke, Cats, Chameleons, Yokohama|
|Dislikes||Himself, His Old Orphanage|
|Ability||Beast Beneath the Moonlight|
|Affiliation||Armed Detective Agency|
|Manga Debut||Chapter 1|
|Anime Debut||Episode 1|
|Japanese Voice||Yūto Uemura|
|English Voice||Max Mittelman|
Atsushi has light gray hair, pale skin, and is of average height with a slim build. He has segmental heterochromia, consisting of purple with yellow along the bottom curve of his pupil. His hair is short and swept forward in loose spikes with a lock left long on the right side of his face. This uneven style is the result of bullying he suffered at the hands of other orphans in the orphanage, and he never fixed it.  Additionally, he has a prominent black streak in his hair.
Initially, he wears rags issued by the orphanage. After he joins the Armed Detective Agency, Akiko Yosano and Doppo Kunikida issue him a white button-up with the sleeves pushed to his elbows, a loose black tie, black pants, black, fingerless gloves, and a suspenders/belt combo with a long stretch of the belt dangling loosely from the buckle.
When he transforms into a partial tiger, his eyes become tiger-eye like and he develops fangs.
Atsushi has severely low self-esteem due to his upbringing. He has a major complex about his worth as a person, as such he reacts negatively to people who judge others as unworthy. When people begin hunting him due to the seven billion yen bounty on his head, he becomes worried and continues to think that he is putting the Agency at risk, though he is told by Kunikida to learn how to become useful rather than worry about the Agency being attacked. As part of his low self-confidence, when confronted with a dangerous situation, he initially tends to cower and/or has difficulty reacting to a situation or understanding what to do, being paralyzed in fear. However, while generally flighty and unsure of himself, his will hardens in tough situations, and he becomes steadfast and reliable. He is selfless and does everything possible to protect his friends, at one point using his body to cover up a bomb to protect the Agency members despite having never met them and on a number of occasions rises up and uses his power to save them.
He is easily scared and is somewhat naive and simplistic, believing things at face value. Despite this, he does have some common sense and is arguably one of the most "normal" members of the Agency. He tends to have exaggerated reactions towards the shenanigans of the Agency members and due to the strange circumstances and situations that follow them.
Although still struggling with his self-esteem, Atsushi gradually improves his confidence and sense of self after joining the ADA, along with his many confrontations with Ryunosuke Akutagawa. Strengthened by several missions and the clashes between the Port Mafia, Guild, and Rats in the House, Atsushi makes a goal for himself: prove his self-worth by helping and saving others, still plagued by the words of his former Headmaster.
He has a strong sense of morality, as seen through his interactions with Kyouka. He values life and tries to help his enemies, such as Kyouka and Lucy Maud Montgomery, both of whom were moved by his actions. He hates it when people die due to unfortunate circumstances or abuse their power to hurt others, as shown during his battle with Akutagawa.
Due to his poor upbringing, he has a mild obsession with money, though never to the point of greed. When he first meets Dazai and Doppo, he agrees to act as bait for the man-eating tiger after learning how much the reward was. When he learned there was a reward for correctly guessing Dazai's original occupation, he comes up with a number of random guesses. He also becomes worried about how much Kyouka eats during their first outing due to the fact he had to pay for it (and she ate quite a bit). Despite this, he willingly helps others in need and money never comes before saving a life.
Beast Beneath the Moonlight (月下獣, Gekka-jū?): Atsushi has the ability to transform into a white tiger. At first, he doesn't seem to have much control over the transformation, likely due to the fact, or caused by, his unawareness of his state as an Ability user.
After becoming an official member of the Agency and under the influence of All Men Are Equal, he gains more control over his transformations - as shown during his second fight with Akutagawa, when he breaks the transformation on his arms to escape.
- Full Body to Partial Transformation: Atsushi has shown several varying states of transformation, which range from a rather large full tiger form, to just slit pupils and tiger stripes on his face. He can transform and manifest various tiger body parts at wills, such as tiger forearms with claws, or a tiger tail.
- Regeneration: Also notable is that Atsushi's ability has extreme regenerative powers capable of healing bisection and amputation almost instantly. This was shown during his fight with Akutagawa.
- Increased speed and stamina: He has shown to possess immense speed, durability, strength, stamina, and endurance on several occasions. He has also been shown to be a natural fighter in close combat and has shown to very cunning in battle in several fights. However, after using his ability, Atsushi seems to become unconscious and collapses onto the ground.
Someone from the underground has put out a 7 billion yen bounty for him with the Mafia - it is later revealed that Fitzgerald is the one behind his bounty and the reason is that Atsushi is a guider to the book that every ability-user desires.
- He and several other characters made appearances in mobile games, such as Love Heaven, Kimito Lead Puzzle 18, and Yumeiro Cast as limited-time characters.
- His favorite food is tea on rice (chazuke).
- His choppy haircut is a result of another child cutting his hair as a prank when he was younger at the orphanage, and he had just let it grow as it is.
- The black streak is completely omitted in the anime but still appears in promotional art and the mobile game.
- When Atsushi Nakajima is wearing his belt, it seems to act like his tail as if he were in tiger form. When Atsushi Nakajima is relaxed, the belt hangs down. If Atsushi Nakajima is surprised or scared the belt is up.