Mamahaha no Tsurego ga Motokano datta

A high school student hopes to move on from a failed relationship by starting anew, only to find their ex at the same school and now as a stepsibling. What was meant to be a fresh start has turned into an unavoidable situation, with the former partner appearing everywhere—home, school, even the same class. The former couple now navigates this new family dynamic, with the ex claiming to be the older sibling. The student refuses to back down, asserting their role as the older brother in the new arrangement. Though they once believed they were meant to be together, they now see each other differently and have accepted they are no longer compatible. For the sake of their parents, they maintain a friendly sibling facade, but the past has changed the nature of their relationship permanently.