Tomoki is Anna's cousin who invites Yuuma to Kawarazaki Manor for their uncle Nawatsuma's birthday. Financially independent and a car owner, he drives the group to the secluded mansion. He openly seethes with hostility toward Yuuma, fueled by a longstanding crush on Anna and the belief that she deserved to be with him instead.

During dinner, Tomoki confronts Nawatsuma directly, labeling him a creep and a jerk. He states that his attendance is merely obligatory and declares his intent to sever all ties, now that he is financially free, planning to relocate with his sister to escape further contact.

In one timeline, after Yuuma and Anna try to leave the manor on foot, Tomoki intercepts them at a bus stop. He taunts Yuuma, insisting that Anna will return to the mansion with him rather than go home with Yuuma. Anna refuses to explain herself to Yuuma, leaving him angered and confused before the time loop resets.

Tomoki has short, wavy brown hair parted to the side and blue, tsurime-style eyes. He stands approximately 173 cm tall with a slim, pale, young-adult build. He typically wears glasses, a necktie, and a suit. His personality is cowardly and perverted. He is a driver and is identified as a non-blood-related son and an older brother in the family.