Shimon Nagareyama, a junior high school student from modern-day Japan, finds himself transported through an old well to the Heian-era parallel world of Kyou alongside his friends Akane Motomiya and Tenma Morimura. His blond hair and blue eyes cause residents of Kyou to mistake him for a member of the Oni Clan, leading to immediate prejudice and confusion.

Identified as one of the Eight Guardians (Hachiyou), Shimon serves as the Suzaku of Earth. His dragon jewel, manifesting on the back of his right hand, grants him his Earth-elemental guardian powers. His primary duty is protecting the Priestess of the Dragon God, Akane, using his abilities to combat the Oni Clan and other threats to Kyou.

Shimon possesses a loyal, kind, docile, and shy personality, tempered by intelligence and optimism. He strives to forge new friendships despite setbacks, forming a significant bond with Akane, who helps him gain self-confidence. While the anime suggests platonic feelings for Akane, other media reveals a deeper emotional attachment where he remains by her side and confesses his feelings.

His abrupt transition from modern Japan to historical Kyou highlights his adaptability and resilience. Being mistaken for an enemy forces him to confront his identity and self-worth, fueling his gradual growth into a more assured and capable Guardian. His supportive relationships with fellow Guardians, especially Tenma and Akane, reinforce his commitment to their shared mission.

Shimon's journey involves overcoming societal prejudice in Kyou related to his appearance, ultimately earning acceptance through his actions and dedication. He evolves from a hesitant outsider into a trusted protector, emphasizing themes of belonging and personal growth within the group.