Raiko is a formidable swordsman allied with Monk Gen'un to defend humanity against Oni forces. He initially protects the temple with unwavering loyalty and acknowledges Jun Tendo as the prophesied savior destined to awaken the dragon Yamata no Orochi.

A concealed personal tragedy defines Raiko's past: Gen'un executed his parents. Jun uncovers this truth during their confrontation and reveals it to Raiko. Despite his steadfast devotion, Raiko remains ignorant of Gen'un's manipulative nature.

Gen'un exploits this loyalty by magically transforming Raiko and his comrades—Kinta, Tsuna, and Sadamitsu—into the Four Heavenly Kings. As god-powered armor stripped of autonomy, Raiko becomes an antagonist compelled to obey Gen'un's orders without hesitation or emotion, even attacking Jun.

Jun's revelation about his parents' execution sparks a fleeting but vital resistance within Raiko, demonstrating his subconscious awareness and lingering humanity. Gen'un instantly subdues this defiance, crushing Raiko to eliminate the threat to his control and shattering the Four Heavenly Kings' power.

After Raiko's defeat, his dagger proves instrumental when Mizuha provides it alongside a gem containing Jun's power. Combined, they forge the sword Jun wields against Gen'un. Raiko's ultimate fate remains undetailed as the narrative shifts to Jun's resolution of the conflict.