Marin Izutsumi is a supporting character in the anime A Ninja and an Assassin Under One Roof, serving as a young mad scientist who operates as an assassin primarily through her inventions. Her background is that of a prodigious inventor who crafts gadgets, tools, and robots for murder, which she uses in her work alongside her nominal assassin profession. She is driven by a competitive rivalry with Konoha Koga, yet this rivalry is laced with a secret admiration that manifests in behavior resembling stalking, such as secretly taking photographs and recording audio of Konoha. Marin designed the robot Roboko specifically to spy on Konoha and eliminate her as competition, though her antagonistic stance eventually softens. Over the course of the story, she transitions from a foe to a reluctant friend of both Konoha and the ninja Satoko Kusagakure, a development that highlights a shift from isolated scheming to reluctant cooperation. Her notable abilities include fighting with mechanical tentacles and various robots, as well as using drugs to maintain a childlike appearance, which serves both as a practical disguise and a reflection of her inventive, unorthodox approach to her work. Her motivations are rooted in a desire to prove her superiority as an inventor and assassin, but her arc reveals a more complex personality capable of forming uneasy bonds with her former targets.