Ekou Houshun'in is a former Karas, once Tokyo's appointed supernatural guardian who abandoned his duty. Disillusioned by human indifference causing youkai decline, he became an antagonist seeking to overthrow the existing order, orchestrating a plan for youkai to dominate humans in a restructured society.

Though human himself, he views humanity as inferior and pursues his goal with unflinching efficiency, justifying his actions as a necessary revolution for Tokyo's preservation. He commands mechanized youkai called Mikura, deploying them across Shinjuku.

Retaining his Karas transformative abilities, his armored form resembles a samurai, embodying his ideological clash with his ninja-like successor, Otoha. Unlike other Karas, he transforms without direct contact with a living Yurine; his artificial Yurine, sustained in a life-support vessel, grants him independence.

His primary scheme involves ravaging Tokyo with mechanical tentacles to absorb energy for his new world, requiring the capture of Nue and her brother to complete his power source. After Nue infiltrates his stronghold, Ekou kills Otoha's Yurine, deeming Nue's capture pivotal. Otoha's intervention, killing Nue and her brother at their request, deprives Ekou of this energy.

In the final battle, Ekou merges with a white dragon but is defeated by Otoha after losing his enhanced abilities. Mortally wounded, he asserts Otoha will eventually understand his perspective. His ultimate fate is ambiguous; a post-credits scene reveals a single discarded boot discovered by an unknown figure.