Seiryū began as an antagonist within the Kitoralsus, a prehistoric race orchestrating monster assaults on humanity. After peace was forged between the Kitoralsus and the Shinkansen Ultra Evolution Institute, he allied with the protagonists to safeguard Japan.

Originating from a Kitoralsus faction that embraced coexistence post-conflict, he became a pivotal bridge between humans and his kind. During the film’s events, he combats extraterrestrial invaders led by Nahane and Ohanefu, leveraging his strategic insight and battle prowess to aid the team.

His pronounced fondness for sweets, especially cake, serves as a recurring tactical tool for others to guide his actions, softening his once-adversarial demeanor with relatable charm.

Evolving dynamics with Hayato and allies underscore his deepening trust in humanity and dedication to mutual objectives. Though the narrative centers on Hayato’s strained bond with his time-displaced father, Seiryū’s arc emphasizes reconciliation and unity, illustrating how former foes can collaborate against shared threats.