Kunihiko Kimishima is a seventeen-year-old resident of the Lost Ground who serves as Kazuma's closest friend, primary source of income, and unwavering supporter. He is a native of the fractured territory and has no family of his own, which makes his bond with Kazuma and the orphan girl Kanami Yuta feel akin to brotherhood. His background as an information broker and businessman defines his early role: he uses a network of contacts to procure valuable intelligence and then funnels mercenary jobs to Kazuma, an Alter user, while deliberately keeping the dangerous details quiet around Kanami. Kimishima's personality mixes a slightly pompous, willfully ignorant surface with genuine resourcefulness, loyalty, and a serious dedication to his work; when he first met Kazuma, he stressed that if Kazuma failed a mission, Kimishima would die, a warning that ultimately proves tragically accurate. Despite possessing no Alter powers, he routinely carries a pair of pistols hidden beneath his sleeves and willingly puts himself in harm's way to protect the Lost Ground from HOLY crackdowns or to defend his friends. He is fascinated with vehicles and always eager to show off his latest roughly built car, though a running consequence of his partnership is that nearly every vehicle he acquires is destroyed—often unintentionally by Kazuma’s Alter-related battles or by other Alter users.

Kimishima’s core motivation is to support Kazuma and ensure the well-being of their small makeshift family. He acts as a grounding presence, injecting a measure of ordinary human courage into a world dominated by superpowered Alters. His most decisive story beat occurs when he and Kanami are captured by HOLD in an attempt to lure Kazuma into a trap. Kimishima steals back his buggy, drives Kanami to safety, and promises to reunite her with Kazuma, even as he himself is shot by pursuing HOLD forces. He hides the severity of the wound, continues to help Kazuma through one final battle, and only after Kazuma carries him back does Kanami’s horrified reaction reveal that Kimishima has died from the gunshot. His death becomes a pivotal turning point in the anime, igniting Kazuma’s overwhelming rage and grief and setting the stage for the climactic Second Uprising. In the manga continuity, however, Kimishima survives the conflict and later marries Ayase Terada, the woman for whom he held an unfulfilled crush in the anime. Even in the anime, his spirit later returns to help Kazuma recover his will to live, underscoring the enduring emotional impact of his steadfast loyalty. Kimishima’s notable abilities lie not in Alter power but in his sharp mind, extensive contacts, vehicular know-how, and the nerve to use his concealed pistols when the situation demands it. He develops from an opportunistic businessman into a quietly heroic figure who ultimately sacrifices himself for those he loves, leaving a permanent mark on the series’ emotional landscape.