Synopsis: My Stepmom's Daughter Was My Ex-Girlfriend

When they were in middle school, a boy and girl fell in love, but their relationship dwindled over time and eventually ended on graduation day. Mizuto Irido and Yume Ayai, the former couple, were taken aback to learn that they were now stepsiblings after their parents remarried. Despite their uneasy past, they agreed to follow a "sibling rule" in order to avoid any awkward situations. However, as they continued to reside under the same roof and have daily encounters, it became more and more difficult to ignore their past and the pull between them. They even had trouble pretending to be siblings while sharing spaces like the bathroom. How long could they keep up the façade?