Buchio Ōishi began life as a male calico cat in the Ōishi household. After two decades, he transformed into a nekomata, gaining the ability to walk upright, speak human language, and grow two tails. This abrupt evolution caused him significant distress, leaving him confused about its cause and uncertain how to navigate his new existence as a youkai. He grew deeply introspective regarding his purpose and future direction in this reborn state. His personality is marked by extreme politeness, emotional sensitivity, and shyness. He frequently apologizes and cries when faced with difficult situations, maintaining formal and respectful behavior even towards his own human family. Physically, he retains feline features, including whiskers and markings above his eyes resembling eyebrows. He refers to himself using the humble pronoun "boku," reflecting his submissive and polite nature. Adjusting to youkai life presented practical hurdles. He completed paperwork for the Youkai Rebirth Registry and sought guidance from local supernatural entities like Jiro, a crow tengu, and Tazenbo. Jiro introduced him to Yuri Tachibana, a kitsune who became his tutor in transformation magic. Under her instruction at "Bakegaku," an academy for youkai, Buchio learned to manipulate his form, such as giving himself human hands. His bond with the Ōishi family remained central, especially with Takumi Ōishi, a fourth-grade boy he views as a younger brother. This familial connection is mutual, and the Youkai Rebirth Registry notes formal adoption by human families as common practice for reborn youkai like him. Yuri occasionally resented him for his stable and loving family, contrasting with her own estranged background. Throughout his journey, he formed significant connections beyond his family. He befriended Chiaki Nishiya, a tsukumogami (animated spirit of a car), while obtaining a driver's license. Chiaki's struggle to care for his aging human owner, Kazuhiko, paralleled Buchio's concerns about purpose and legacy. Encounters with figures like Sanmoto Gorozaemon, a demon king and youkai leader, provided philosophical guidance. Sanmoto shared stories, such as that of Suzu, a nekomata who overcame hatred, to illustrate paths toward finding personal meaning. A pivotal moment demonstrating his growth occurred when he saved Takumi from a nue, a dangerous mythical creature. Despite his typically fearful nature, he intervened protectively, later crying from relief and residual terror. This incident highlighted his deepening courage and commitment to his family. During a major crisis involving otherworldly oni invasions and the disappearance of kotodama (the power of words and belief) – which threatened the existence of gods and youkai – Buchio faced these apocalyptic events alongside the community. The resolution, achieved through the restorative power of kotodama fueled by love and memory, reinforced his place within the interconnected world of humans and supernatural beings.