"The weak will die. Die, and make way for others."
Akutagawa has a slim build and very pale skin. He's often seen covering his face with his hand due to his frequent coughing. He has short, choppy black hair with side bangs that reach his chin and turn white at the tips. His eyes are sharp, somewhat baggy, and a dark empty grey.
He wears a long, black coat reaching past his knees over black fitting pants and black dress shoes. Underneath his coat, he dons a white dress shirt, decorated with a layered ruffled fabric. He also wears a white cravat.
Akutagawa has a black and white Social Darwinist view of the world, and claims that weak people should die and give way to the stronger ones. He is not afraid of pain and defeat, if only to hear a word from a "certain person". His ruthless, vicious nature makes him one of the Port Mafia's most dangerous members, feared by both ally and foe. Much of the obedience he receives from subordinates of Black Lizard largely stems from fear of his short temper and general intolerance of incompetence.
Self-titled Port Mafia's "dog", Akutagawa depicts an acute willingness to commit violent crimes to further not only the mafia's goals but his own agenda. Merciless and blunt, Akutagawa doesn't discriminate when it comes to his targets, having no qualms killing anyone from innocent civilians, children, and enemies alike. Hostile as he is towards the weak, he dislikes meaningless torture and prefers killing in one go whenever possible.
As violent as he is, Akutagawa maintains a generally composed and detached approach. Towards subordinates and superiors alike, he acts aloof, distancing himself from social interactions however possible. Nonetheless, his composure is fragile. In instances such as Higuchi's screw-up during the manhunt for Atsushi Nakajima Akutagawa is quick to lash out, ridiculing her for risking the bounty by acting recklessly. This quick temper often gets in his way, fueling his actions to the core of his very being.
The center of this anger stems from his past as an orphan in the harsh slums of Yokohama. Since childhood, Akutagawa's grim outlook never changed. The only thing that changed was meeting Dazai when he was 14, already willing to kill a group of illegal traders responsible for murdering his companions. This meeting with Dazai ends in a pivotal change in Akutagawa - respect for someone. Even after undergoing Dazai's extreme and horrific training, Akutagawa never wavers from his own philosophy, starkly against adopting Dazai's value of information over simply getting rid of the mafia's enemies. Having only heard Dazai's berating, learning of Dazai's high opinion of Sakunosuke Oda damages Akutagawa on a deep level, feeling insulted he is thought of as lower than someone who refuses to kill in the mafia. Dazai's defection deepens the damage, leaving a permanent, lingering sense of inferiority in Akutagawa's mind no matter what he accomplished in the mafia. Although still striving for Dazai's approval, Akutagawa nonetheless views Dazai's current disposition as a disgrace to the bloodstained reputation he carved into Port Mafia's history.
Akutagawa's desire for Dazai's approval inevitably leads to an intense resentment towards Dazai's new "student", Atsushi. First meeting Atsushi when he's weak, easily scared, and freezes in the face of violence, Akutagawa dismisses Atsushi as nothing more than another weak person destined to die for the sake of those stronger than him. Although Atsushi's tiger transformation momentarily gives him a rush, Akutagawa nonetheless sees nothing special in Atsushi. His opinion of Atsushi worsens when Dazai boasts about him, simultaneously insulting Akutagawa's worth as Dazai's former pupil. For much of the time, Akutagawa cannot understand the value others put in Atsushi, and vice versa. Atsushi is a walking paradox to Akutagawa - weak, but acting stronger than he actually is for a place in the world and permission to live, despite being so valued by others. This conflicts deeply with Akutagawa's self-perception. Others see him as powerful, but Akutagawa doesn't acknowledge his strength as a result of his upbringing and own philosophy. This leads to repeating the hypocrisy of condemning Atsushi for attempting to get everyone's approval when Akutagawa himself acts almost entirely for Dazai's approval.
This rivalry eats at the two for much of the time, however, Akutagawa eventually comes to something of an understanding of Atsushi. His resentment still fresh, and a never-ending willingness to kill Atsushi for his own sake, at the least mingles with some form of respect towards Atsushi. This shows most notably when Atsushi struggles to come to terms with the death of the orphanage headmaster. Although it is the perfect time to off Atsushi, Akutagawa refrains from doing so, saying he'll leave him alone to deal with the pain of losing his mentor. He also develops an adept understanding of Beast Beneath the Moonlight, aiding both of them when fighting together against Fitzgerald and Ivan.
For all his rage, bitterness, and resentment towards humanity and the world itself, Akutagawa has his moments. He has an amicable relationship with his younger sister, Gin, going as far as to help and do her favors without complaint. Further, after Higuchi and Black Lizard save him from a rival group, Akutagawa apologizes to Higuchi for the trouble. Although these are small, short moments of Akutagawa's calmer, earnest side, they nonetheless carry weight. It's evident Akutagawa rarely or never lies, making him honest, even if it's a brutal and unnecessary majority of the time.
- He is very strict in conserving electricity. 
- Akutagawa's ability, Rashōmon, turns his coat into a black beast. This is in reference to the Japanese author Ryunosuke Akutagawa's short story titled Rashōmon wherein a homeless servant stole the clothes of an old lady by ripping it off her.
- According to the Bungo Stray Dogs official Twitter, he does not know the name of the "frilly thing" on his collar (cravat).
- Along with several other characters from the series, Akutagawa made an appearance in the mobile game Love Heaven as a limited-time character. He also made an appearance in the mobile game "Kimito Lead Puzzle 18" as a stage boss and as a limited-time character.