Raikou Minamoto serves as a noble warrior in Japan's Heian period during the Shōryaku and Chōtoku eras, commanding a critical military role protecting Kyoto from disease outbreaks, political unrest, and bandit incursions. His responsibilities involve leading security operations during periods of instability. While on duty in Sagami Province, he rescues a young girl named Kintoki from a fatal family coup orchestrated by her uncle. He brings her to the capital under his guardianship and integrates her into his elite warrior unit, the Four Heavenly Kings (Shitennō), where she is raised and trained in combat while concealing her gender.

As Kintoki matures within his ranks, Raikou maintains a close bond with her. Their relationship develops unspoken emotional complexity that remains unresolved through their interactions. Five years after Kintoki's rescue, Raikou continues defending Kyoto against escalating threats, including bandit raids from Mount Oeyama. These attacks are later exposed as part of a broader conspiracy led by Fujiwara no Michinaga to exploit chaos for political gain, including plots to burn the capital. Raikou confronts these dangers alongside his warriors, including Kintoki.

When Kintoki is abducted by the bandit leader Shuten Dōji—revealed as her cousin Ohni-hime—Raikou spearheads a mission to infiltrate the Mount Oeyama stronghold, reaffirming his commitment to her safety as her protector. The character draws inspiration from the historical samurai Minamoto no Yorimitsu (Minamoto no Raikō), a Heian-era commander who led the Shitennō warriors, including Sakata no Kintoki, against supernatural adversaries and rebels, aligning with Raikou’s depicted leadership and combat duties.