Shun, a new student struggling to fit into his new school environment, finds himself slipping into a mild depression. His life takes an unexpected turn when he encounters a group of classmates near an eerie, Western-style mansion known as the “Jailhouse,” rumored to harbor a terrifying blue creature. Before long, Shun, along with Anna and four other students, become ensnared within the mansion’s walls. Together, they must find a way out before the monstrous inhabitant discovers them.