My Stepmom's Daughter Is My Ex

Since they shared a love of reading, slacker Mizuto Irido and reclusive nerd Yume Ayai seemed to be a match made in heaven. Sadly, as their differences deepened over time, they split up right after their middle school graduation. However, by some divine comedy, the two are reunited as step-siblings. The previous pair develops a rivalry since neither of them wants to accept the other as the older sibling. In an effort to "fix" the problem, Mizuto and Yume come to an agreement on a rule: the winner will not only be referred to as the older sibling but will also be given the right to make requests. But now that they share a home, their lingering memories begin to affect how they behave, maybe rekindling feelings that weren't entirely put to rest in the first place.