Toshiko Hazuki, father to protagonist You Hazuki, works as a professional photographer. Returning from an extended assignment in Peru, he brings home an adopted son named Sunny, who becomes You's younger stepbrother. Sunny forms a strong attachment to both Toshiko and You.

Toshiko strongly opposes You's involvement in volleyball. This resistance originates from unresolved personal trauma tied to his ex-wife, Kyushi Tajima (also referenced as Kanako Tajima), who abandoned the family to pursue her volleyball career when You was very young. To shield You from this painful reality, Toshiko deliberately led her to believe her mother died. His discomfort surfaces whenever You watches Kanako Tajima's volleyball commentaries on television or encounters her image.

His parenting includes moments of volatility, exemplified when he slaps You during an argument, prompting an unexpected and defiant slap in return from her. Over time, Toshiko experiences significant development. He gradually softens his stance on You's athletic ambitions, ultimately becoming supportive of her volleyball career. This shift occurs after You discovers the truth about her mother's abandonment and confronts the associated emotional turmoil.

Toshiko's relationship with Sunny reflects a caring dynamic, with Sunny frequently following both him and You. Information regarding Toshiko's presence or development in sequel series, spin-offs, OVAs, or other expanded media related to the franchise does not exist.