Desperate for her only son Tatsuya to pass his college entrance exams after two failed attempts, Ryouko spends every evening soothing his exhausted body during their shared bath. One day, their bathroom suddenly breaks down, and the repairman who arrives is Nakajima, Tatsuya's classmate and a confident, mature young man working as a gas technician. Surprised yet intrigued, Ryouko begins to realize there's more to life than just academics as she's drawn to Nakajima's self-assured presence. That night, mother and son bathe together again, but Tatsuya senses a change in his mother's behavior—and begins to suspect something is different.