Kippei Nagatsu hails from Aichi Prefecture, instantly recognizable by his spiky blue hair and heavy build. He shares an unbreakable childhood bond with Kakeru Miwa, rooted in mutual tragedy: both lost their parents young, with Kippei as the sole survivor of an Oni attack that claimed his family. This forged a brotherly connection between them.

In his youth, Kippei radiated cheerfulness, embracing peaceful hobbies. He cultivated a passion for occult subjects, tokusatsu, and anime—interests first sparked by Kakeru but pursued independently. During high school, he actively sought social reinvention as a popular figure, though these attempts yielded little success.

Throughout the war against the Oni, Kippei serves in a critical support role. Devoid of supernatural powers or technological augmentations, he remains the only non-enhanced member of his team. Despite this, his steadfast reliability and encouragement—especially toward Kakeru—prove indispensable. He provides vital stability during Kakeru’s volatile initial encounters with the Yoroi powered suit and the entity Ibara, curtailing berserk episodes.

Kippei undergoes profound growth amid the conflict, evolving from a lighthearted friend to a resolute combat ally. He demonstrates unwavering courage in perilous situations and fierce loyalty in protecting targeted friends like Ōka Myōjin. His involvement extends to pivotal confrontations, including the exposure of Ōka’s father Masanori Myōjin’s role in unleashing destruction. After Masanori’s defeat, Kippei continues life alongside his friends, finally liberated from looming threats.