Kei Matoba, a former Japanese Self-Defense Force soldier, now serves as a detective sergeant in the San-Teresa Metropolitan Police Department. His military past is shadowed by combat in Semanian territory, where a lone assailant nearly decimated his unit, forging a deep-seated animosity toward beings from the otherworld. This bitterness initially fuels his distrust of "aliens," yet his partnership with Tilarna Exedilica, a Semanian knight, slowly tempers his prejudice.

A decade-old tragedy—the death of his younger sister—lingers beneath his guarded demeanor, shaping his protective instincts. His career is equally marked by loss: the death of partner Rick Fury during a disastrous drug bust involving a kidnapped fairy ignites a vengeful drive and reluctance to collaborate with Tilarna, whom he is forced to work alongside.

Stubborn and sharp-tempered, he navigates cases with tactical discipline and streetwise resourcefulness, skirting regulations or leveraging underworld contacts like informant Biz O’Neill to close investigations. Though he chafes at protocol, a grudging respect for order persists. His dynamic with Tilarna shifts from clashing outsiders to allies bound by unspoken trust, even as he masks concern behind curt exchanges.

An amicable yet complex tie remains with Cecil Epps, a deputy coroner and former lover who harbors unresolved feelings. His growth emerges through confronting Zelada, the Semanian mage behind his unit’s destruction. Their final clash, ending Zelada’s reign, becomes a turning point: he sheds old hatreds, committing to mend fractures between humans and Semanians.

Defined by a sardonic wit, silent guilt, and a results-over-rules ethos, his journey traces a path from embittered isolation to resilient collaboration, anchored by his bond with Tilarna and a resolve to uphold justice in a divided city.