Muneto Ungyosai is a timid college student from a family steeped in religious tradition; his father serves as a Buddhist temple master, shaping Muneto's upbringing within a spiritually focused environment.

He shares a profound personal bond with Kayo Asakura, his high school romantic interest. Her unique physiological compatibility marks her as a prime target for the invading alien Demon Beasts, driving Muneto's deep involvement in the conflict.

As a junior operative of the Interplanetary Mutual Observation Agency, Muneto begins inexperienced in combating the Demon Beasts. His initial missions focus on disrupting the aliens' goal to impregnate human females and create hybrid rulers for Earth.

Following the death of his mentor, Shin'ichi Kasu, Muneto partners with the ambitious agency operative Jun'ichi Yagami. Together, they pursue the Hybrid—Kayo's rapidly maturing offspring with the alien Vanguard—whose existence accelerates the invasion.

Muneto's family directly engages in the conflict; his father interprets the alien incursion through the lens of familial karma, while his uncle, Munechika Ungyosai, provides martial support against the Hybrid.

His missions extend beyond Tokyo, including operations in Hong Kong to disrupt Hybrid collaborations with the Pearl River Triad, and interventions during a Ryukyuan islands school trip where the Hybrid targets Kayo once more.

Muneto evolves from timidity to determined resistance, though his effectiveness remains challenged by the overwhelming Hybrid threat and invasion scale. His final depicted actions involve collaborating with agency enforcer Irimote to rescue Kayo, leaving his ultimate fate unresolved.