Yoshio Kobayashi, known almost universally by his surname Kobayashi, is a main protagonist of Rampo Kitan: Game of Laplace. He is a thirteen-year-old middle school student whose life is defined by a profound and chronic boredom. His ordinary existence is shattered when he wakes up in his classroom to find his homeroom teacher brutally murdered and himself holding the weapon, making him the prime suspect. Kobayashi is characterized by his extreme emotional detachment and lack of interest in others. He views the world as a dull place populated by anonymous gray silhouettes who only gain definition when they become relevant to a mystery, and he lacks typical empathy for human suffering. This makes him a uniquely disquieting protagonist. His primary drive is the pursuit of excitement and the alleviation of his boredom. The murder investigation is the first thing that has ever truly engaged him, and he quickly becomes addicted to the thrill of solving macabre mysteries. After proving his innocence, Kobayashi volunteers to become the assistant of the genius detective Kogoro Akechi. He finds in Akechi a kindred spirit of intellectual isolation, viewing the detective's work as an endless source of stimulation. His best friend, Souji Hashiba, represents his connection to normalcy and acts as his protective moral compass, often trying to shield Kobayashi from the shocking cases they encounter but ultimately supporting his friend's newfound passion. Throughout the series, Kobayashi evolves from a passive, bored observer into an active participant in the world of crime-solving. He develops a sense of purpose defined not by social norms, but by the intellectual stimulation of the game of detection. He confronts the nihilistic philosophy of the vigilantism of Twenty Faces, ultimately finding meaning in the chaos of human unpredictability rather than in deterministic order. Kobayashi possesses a sharp, analytical mind capable of seeing through deception and connecting clues. His emotional detachment allows him to remain calm under extreme pressure, and he is remarkably brave and resourceful, willingly putting himself in dangerous situations, such as disguising himself as a girl to act as bait for a kidnapper, in order to aid the investigation.