Raikou Minamotono commands the Four Heavenly Kings, a noble samurai order safeguarding Heian-era Kyoto amidst banditry, political treachery, and plague. During a violent coup orchestrated by Yoshinobu that annihilates Kintoki's family, Raikou discovers the young girl disguised as a boy fleeing into the mountains. Recognizing her latent strength, he rescues her and brings her to the capital. Under Raikou's guidance, Kintoki trains rigorously in combat and swordsmanship, joining his warriors under the new identity Kaidohmaru.

As Kintoki matures into a formidable fighter, an unspoken bond deepens between her and Raikou, transcending their mentor-student relationship. Raikou leads his warriors with unwavering duty and strategic brilliance against escalating threats to Kyoto. A significant menace arises from Ohni-hime (later Shuten Dōji), Kintoki's cousin and Yoshinobu's daughter. Ohni-hime commands bandits from Oeyama, allying with the ambitious Fujiwara no Michinaga to undermine the capital. Unaware Kintoki is female, Ohni-hime obsessively seeks to "rescue" her cousin, triggering violent clashes. Raikou coordinates the defense against Ohni-hime's onslaught, which culminates in Kyoto burning and Kintoki's abduction.

In the final confrontation, Raikou assaults Ohni-hime's Oeyama fortress to save Kintoki. His ultimate commitment to protecting Kyoto demands a sacrificial death, securing the capital from Ohni-hime's destruction. This final act cements his legacy as a devoted guardian, shaping Kintoki's enduring role as Kyoto's protector in his stead.