Ryuken, born Ramon Kasumi, was the younger half-brother of Kenshiro Kasumi, sharing a father but different mothers. He first appeared as Ramon in earlier stories, protecting Aya Kitaōji from attackers and serving as bodyguard for Pan Yuling against the Tàihú Bāng gang during her time in Japan. Witnessing the birth of his adoptive son Kenshiro in 197X solidified his Hokuto Shinken lineage; he named the child after his half-brother due to their shared Big Dipper-shaped birthmark. Ryuken regarded Kenshiro Kasumi as the strongest Hokuto Shinken warrior, comparing his might to "the blue sky above."

As the 63rd successor of Hokuto Shinken, Ryuken upheld its strict single-successor tradition. He clashed fiercely with Kōryū for succession rights and emerged victorious. Later, he adopted four orphans—Raoh, Toki, Jagi, and Kenshiro—training them in Hokuto Shinken at his temple. Raoh showed immense potential but harbored conquest ambitions, while Toki developed a pacifist, healing-focused style called Hokuto Ujoken. Ryuken ultimately named Kenshiro his successor, provoking Raoh's rebellion.

During a confrontation where Ryuken tried to seal Raoh's rebellious fighting fist, he suffered a sudden heart attack. Raoh exploited this weakness, killing him. Ryuken's students initially attributed his death to illness, concealing Raoh's betrayal. Toki revealed the truth during Kenshiro and Raoh's first battle. Ryuken's teachings lingered as a spiritual guide; both Kenshiro and Raoh reflected on his wisdom during critical moments, such as Raoh recalling Ryuken's warning against succumbing to rage when provoked by Juza.

In the *Legends of the True Savior* film series, Ryuken appears in flashbacks and thematic narratives, reinforcing his role in shaping the protagonists' paths. His legacy is further explored through his philosophies' impact on Kenshiro's resolve to protect the innocent in the post-apocalyptic wasteland.