Ryuken, born Ramon Kasumi, ascended as the 63rd grandmaster of Hokuto Shinken, a martial discipline honed to exploit an adversary’s vital points. Adoptive father and mentor to Raoh, Toki, Jagi, and Kenshiro, he dedicated his early years to shielding figures like Aya Kitaōji and Pan Yuling from danger, as chronicled in prequel accounts. These tales also unveiled his kinship with Kenshiro Kasumi—half-brothers sharing a father but distinct mothers.

After taking the brothers under his wing, Ryuken rigorously trained them in Hokuto Shinken’s lethal techniques. His designation of Kenshiro as heir ignited strife with Raoh, whose ambition flared into rebellion. During a clash where Ryuken moved to suppress Raoh’s power, a sudden heart attack felled the grandmaster, enabling Raoh’s fatal strike. Though Kenshiro initially accepted Ryuken’s death as natural, Toki disclosed the grim reality amid Kenshiro’s inaugural duel with Raoh.

Ryuken’s legacy persisted through flashbacks that guided the brothers’ choices in pivotal moments, underscoring his teachings and their lingering discord. Expanded lore detailed his naming of Kenshiro—inspired by a Big Dipper-shaped birthmark—and his defense of refugees fleeing the Land of Shura, reflecting his dedication to Hokuto’s principles. His past rivalry with Kōryū over succession rights and his struggle to temper the art’s lethality with morality further defined his tenure. Though absent in later years, his ideals endured, molding Toki’s nonviolent philosophy and Kenshiro’s unwavering vow to shield the weak.