Shimon Nagareyama, a modern-day Japanese junior high student, is transported to a Heian-period parallel world with friends Akane Motomiya and Tenma Morimura. His blond hair and blue eyes—resembling traits of the feared Oni Clan—spark distrust among locals, leading to social challenges and hostility in the ancient capital.

As the Earth Suzaku among the Eight Guardians, Shimon bears the dragon jewel on his right hand. His Earth elemental attribute aligns with his duty to protect Akane, the Priestess of the Dragon God. Despite insecurities about his appearance, he displays unwavering loyalty and courage against Oni Clan threats and vengeful spirits.

His bond with Akane evolves across narratives: the main anime depicts supportive friendship, while his dedicated ending reveals romantic feelings, culminating in a confession and choice to remain with her. His friendship with Tenma offers mutual support as fellow outsiders. Initial prejudice from Inori, a fellow Guardian who despises Oni, gradually shifts through shared battles.

In the *Maihitoyo* arc—spanning film, game, and stage adaptations—the Guardians aid Akane during a palace-wide spiritual corruption crisis, where she navigates court politics with assistance from new ally Suefumi Oono. Shimon appears in spin-offs like *Hyakuman-nin no Harukanaru Toki no Naka de* and stage productions.