Keisuke Naoto possesses fair skin, messy black hair, and prominent eye bags—a constant mark of sleep deprivation fueled by watching performances of the idol group Dog Play. He consistently wears Dog Play merchandise, a clear badge of his intense fandom. His personality blends naivety, laziness, and aggression. This naivety drives his persistent attempts to befriend Kaname Asagiri, even in the face of Kaname's overt hostility. Laziness manifests as a refusal to address his personal debts. Aggression surfaces instantly whenever his idol-watching sessions are interrupted. His entire existence revolves around Nijimi Anazawa of Dog Play, whom he obsessively calls "my Nijimin." This fixation compels him to seek revenge upon learning Kaname killed Nijimi, leading to his attempt to murder Kaname. Instead, Kaname uses Nijimi's magical Stick to force Keisuke to carve out his own heart with a knife, making Keisuke Kaname's first kill. The manga depicts Keisuke initially trying friendship with Kaname, contrasting the anime's portrayal where he harbors immediate anger over Nijimi's corruption. His hobbies include attending Nijimi's fan events, collecting oshiringo products, and practicing wotagei. He enjoys noodles and tsukemen but dislikes criticism of other idols. Family life involves only his mother; the absence of his father suggests divorce or death. A significant alternate timeline in Chapter 136 reveals Keisuke never became a Dog Play fan because Nijimi avoided misfortune. Consequently, he never obsessed over her, avoided his vengeful path, and was not killed by Kaname. In this reality, he enjoys a happy romantic relationship, potentially leading to marriage, and never met characters like Sakura Sakaki. Further details include his birthday on August 12, a Leo zodiac sign, and name etymology combining "gemstone" (圭) and "forerunner/herald" (介) for Keisuke, and "straight" (直) and "door" (戸) for Naoto.