Ryunosuke Sakamoto, son of Shinsengumi president Oryo, spent his formative years from age ten in Shanghai for education and worldly experience before returning to Kyoto. He is constantly accompanied by Nekomaru, his 300-year-old bakeneko yōkai companion, officially registered under laws requiring licensing for human-supernatural coexistence.

His personality mixes peculiar humor with earnest dedication to the Mobile Shinsengumi's mission of enforcing yōkai regulations. He navigates romantic situations with noticeable awkwardness and holds a subtle crush on fellow member Yuko Kondo, which sometimes colors his group interactions.

A defining trait is his repeated deaths, often stemming from accidental or comedic mishaps, followed by immediate resurrections. Nekomaru uses his nine-life ability to transfer souls, reviving Ryunosuke each time, establishing a recurring cycle of demise and recovery. The most significant incident occurs when Nekomaru's soap-related clumsiness causes Ryunosuke's death. During revival, Nekomaru inadvertently uses a female soul, causing Ryunosuke to temporarily inhabit a female body. This transformation brings social and practical difficulties, including unwanted attention and mistaken identity, until another death and resurrection returns him to his original form.

His relationship with Nekomaru is central, defined by mutual loyalty despite the yōkai's role in his misfortunes; Nekomaru's protective nature drives him to seek Ryunosuke's happiness. Conversely, tension exists with his mother, Oryo, particularly concerning potential plans for his return to Shanghai, which causes her emotional distress. Ryunosuke also receives romantic attention from another Shinsengumi member, Kaoru Okita. Additionally, Yuko Kondo actively schemes to foster a relationship between him and local waitress Sayoko, aiming to keep him rooted in Kyoto.