Fuyuhiko Kuzuryū, heir to Japan's largest yakuza syndicate, the 30,000-member Kuzuryu Clan, was exposed to extreme violence from childhood. This included witnessing near-lethal fights between his parents that sometimes endangered him. He hardened early, ceasing to cry by second grade and accepting his family name's association with death. His assigned protector, Peko Pekoyama, shielded him during these incidents and joined him on childhood adventures like surviving a kidnapping and escaping after becoming lost in the mountains. Despite their bond, Fuyuhiko resented Peko viewing herself as merely his "tool," insisting he valued her as an individual. His assertive younger sister, Natsumi, was seen by clan factions as a more suitable heir, but she refused the role, declaring she only excelled as "Fuyuhiko's sister." Natsumi's murder by Hope's Peak Reserve Course student Sato drove Fuyuhiko to retaliate by killing Sato with a metal bat, an act that deeply affected his class's morale.

Scouted as the Ultimate Yakuza, Fuyuhiko enrolled in Hope's Peak Academy's Class 77-B alongside Peko, instructing her to conceal their relationship and interact as ordinary classmates. Initially distant and confrontational, he avoided socializing and openly threatened others, emphasizing his yakuza background to compensate for insecurities about his short stature and "baby face." He still attended classes regularly and participated in group activities like classroom repairs and electing a class representative. He respected his homeroom teacher, Chisa Yukizome, for her efforts to unify the class. After Natsumi's death, he revealed quiet concern for Peko, such as helping her gather belongings, noticed by classmates. During Junko Enoshima's escalating "Tragedy," Fuyuhiko joined searches for missing classmates and rushed to Peko's side when Mukuro Ikusaba injured her, vowing revenge. Unwittingly lured into Junko's trap, he witnessed Chiaki Nanami's execution via brainwashing video, converting him and his class into Ultimate Despair.

During the Killing School Trip on Jabberwock Island, Fuyuhiko maintained isolation, refusing group events and verbally attacking others. His relationship with Peko resurfaced when she killed Mahiru Koizumi to protect him from his own murder plot, taking full blame. At her trial, he tearfully confessed he never saw her as a tool but as a person he needed, pleading for her life. Her execution cost him his right eye. This trauma ignited transformation: he apologized to Hiyoko Saionji for his role in Mahiru's death through a harakiri-style self-stabbing, demonstrating remorse. He gradually integrated, showing concern for others like Nagito Komaeda during the Despair Disease and intervening to protect Sonia Nevermind from harassment. Free Time Events with Hajime Hinata revealed deeper insecurities—he felt unworthy of his "Ultimate" title, lacked traditional yakuza traits like tattoos, and secretly enjoyed sweets like karinto, which he deemed unmanly. Hajime became his first genuine friend, helping rebuild his self-worth.

After the Neo World Program, Fuyuhiko survived as a remnant of Ultimate Despair. Captured by the Future Foundation, he was rehabilitated and later resided on Jabberwock Island to atone. He joined classmates to prevent Ryota Mitarai's hope brainwashing video, embracing responsibility for his past actions as Ultimate Despair. His development culminated in a commitment to personal strength—dedicated to reshaping his clan through merit rather than birthright and valuing connections forged through shared hardship.