Ryūto Sakurai, biological son of Kanako Sakurai and the late Suwa Takumi, entered the world nine months after his father died attempting to rescue a cat. Raised closely alongside Tōko Amano's family due to his mother's deep friendship with Yui Amano, he became Tōko's foster sibling after Kanako adopted her following the car accident that killed Tōko's parents.

Ryūto professes to be the reincarnation of his father, Takumi Suwa. He asserts Takumi fell in love with Tōko's mother, his "first love," and supplied the poison used in the fatal car accident. Mirroring his claimed past life, Ryūto pursues multiple older women simultaneously, exhibiting similar romantic patterns and expressing a preference for partners harboring "dark feelings" or perceived as "dangerous."

Characterized as a womanizer, Ryūto manipulates relationships to gather intelligence. He leverages connections forged through these romantic involvements to report on Tōko's activities and relevant events, even using his network to pressure Konoha Inoue into writing novels by threatening Tōko's potential disappearance. His relationship with Hotaru Amemiya concluded with her death, and he later initiated a long-term relationship with Chia Takeda during the "Parumiere" storyline.

Ryūto is the father of a son named Yuuto. His familial relationships include his mother Kanako, his deceased father Takumi, his half-sister Tōko Amano, and his son.