Yuuma travels with his girlfriend Anna to the secluded Kawarazaki Manor in the mountains to celebrate the birthday of its master, Nawatsuna, and to meet Anna's cousins, Maki and Tomoki.

He initially presents an ordinary personality, though he harbors underlying insecurities in his relationship with Anna. His interactions with Tomoki are strained due to Tomoki's lingering affections for Anna and open hostility toward him.

His reality shatters when he becomes trapped in a time loop, forced to relive the events at the mansion while retaining the memories of each repetition. This endless cycle grinds down his ordinary demeanor, forging him into someone increasingly aggressive, possessive, and desperate to escape the nightmare and protect his relationship.

His driving motivation is to find a way to break the loop and flee the mansion with Anna, preserving their sanity against its disturbing events and the manipulations of its residents. He must overcome his own deep-seated insecurities and passivity to effectively confront the mounting threats.

A pivotal moment occurs in one loop where he and Anna seemingly achieve escape, only for her to inexplicably return to the mansion with Tomoki, leaving him behind. This perceived betrayal sears into him, profoundly affecting his actions in the cycles that follow.

His progress becomes a grim process of trial and error, uncovering the mansion's secrets and discovering specific triggers to advance. The knowledge painstakingly accumulated through countless repetitions eventually allows him to navigate the horrors with grim efficiency, pushing him toward a final resolution.