Sayako has been in a relationship with Naohiko for 10 years, but the passion of love faded long ago, and the couple starts to slowly crumble. But one day, Sayako finds in the street a staircase she'd never seen before. Climbing them. she travels 10 years into the past when Naohiko was still a teenager - in a world where her teen self doesn't exist. This is the start of a strange love-triangle between Sayako, Naohiko as an adult, and Naohiko as a teenager.