Mamahaha no Tsurego ga Motokano datta

Mizuto Irido and Yume Ayai were a match made in heaven, connected by their mutual love for literature; however, their differences gradually grew, and the two separated just after middle school graduation. But fate had other plans, and the two were unknowingly reunited as step-siblings.

Rivalry began to brew between the former couple, both unwilling to acknowledge the other as the older sibling. In order to settle the dispute, they agreed upon a rule: whoever crossed the boundaries of siblinghood norms would lose, and the winner would get to make a request. Despite their rivalry, living under the same roof reminded them of the memories they shared, possibly rekindling the feelings that were never fully extinguished.