Eisen serves as the Genbu of Heaven among the Eight Guardians. He is the Emperor of Kyou's younger half-brother who renounced his imperial position to embrace monastic life, reflecting his aversion to conflict and preference for spirituality. His personality blends gentleness, thoughtfulness, and timidity. Deeply introspective, Eisen frequently grapples with self-doubt about his worthiness as a Guardian. Despite his reserved nature, he exhibits unwavering loyalty, particularly toward Akane, the Priestess of the Dragon God. He develops profound romantic feelings for her, creating internal tension between his monastic vows and personal emotions. This devotion runs deep enough that he would sacrifice his life for her safety.

An accomplished flutist, Eisen finds solace in his music and employs it in spiritual contexts. His elemental affinity is Water, and his dragon jewel resides in the palm of his left hand. As a Guardian, he combats supernatural threats, primarily utilizing supportive and purification abilities aligned with his spiritual background.

During the events of *Maihitoyo*, Eisen actively supports Akane as curses overwhelm the Imperial Palace. He joins efforts to purify the palace and counter the Demon Clan's influence, participating in mirror realm battles where his abilities aid the group. He witnesses Akane's struggles with her duties and her isolation caused by noble bullying. Alongside the other Guardians, he supports her through these challenges and her quest to purify the palace with the mysterious young man Suefumi.

Eisen's character arc consistently explores balancing his peaceful inclinations against his imposed Guardian responsibilities. His background as former royalty informs his nuanced perspective on power and duty, while his emotional journey centers on reconciling his spiritual path with his human attachments.