Motjirou Kajii is a supporting villain and a low-rank member of the Port Mafia in the anime and manga series Bungou Stray Dogs. He is a direct reference to the Japanese poet with the same name.
Motojirou's history is never described in detail. It is known that he is a wanted terrorist bomber responsible for dozens of civilian deaths in the city of Yokohama. It is unknown if this was done while working for the mafia or was on his own accords.
His first appearance is on a mission to capture Atsushi (due to a bounty offered by The Guild) while he and Akiko Yosano of the Armed Detective Agency were on a public subway train. Motojirou and Kyouka Izumi, who is wearing a high explosive vest, are sent by Akutagawa Ryuunosuke to the train. Motojirou takes the driver's announcement module and tells the train that they will perform a "science experiment" before creating an explosion on one of the carts that killed 2-3 civilians. Akiko Yosano confronts and defeats Motojirou while Atsushi confronts Kyouka and talks her out of blowing up the train. The mission fails and it is unknown if Motojirou was arrested or somehow escaped.
Later, when the three-way battle with The Guild starts, Motojirou and Akutagawa Ryuunosuke attack a Guild ship being loaded by Nathaniel Hawthorne and Margaret Mitchell. Motojirou lets himself be captured but utilizes the arrogance of Nathaniel and Margaret to take them by surprise. He and Akutagawa successfully destroy the ship along with several guild workers and knock Margaret out of commission, but Nathaniel gets away and returns to The Guild.
After the war with The Guild, when Fyodor Dostoevsky sets up a plan to have the Port Mafia and Armed Detective Agency destroy each other, the ADA raid the Port Mafia, and Motojirou is assigned to defense. He successfully forces the ADA to retreat before forming another plan.
Motojirou Kajii comes off as extremely eccentric and seemingly psychopathic. He has an unhealthy obsession with "science" and considers his bombing of innocent civilians to be for scientific purposes.
He has no care for human life in general but has a deep obsession with death. He has paused mid-fight and talked to his would-be victim specifically to ask about what death is like.
- Lemon Bomb(In Japanese: 檸檬爆弾, Remonēdo): Motojirou's special ability. Despite common misinterpretation, his ability is not actually the bombs he uses themselves. It simply gives him complete immunity to lemon shaped bombs. This allows him to strap bombs to himself and blow up enclosed spaces without any risk to himself.
- Bomb Creation: He is adept at creating small bombs in the shape of lemons. One bomb is more than enough to kill someone, but structural damage is relatively limited. When he stacks them, he is capable of destroying bigger structures.