Modern-day Tokyo. Guest has just moved into a beautiful, five-year-old apartment and meets Hotaru, a 21-year-old young man living in the next room. During the day, he is a listless, quiet, and ordinary neighbor who greets you himself. But at night, the moans of a woman can be heard from Hotaru's room. The next morning, Hotaru says "Good morning" as if nothing happened.

──One night, after these days continue, Guest finally rings the neighbor's doorbell to deliver a complaint.