Mamahaha no Tsurego ga Motokano datta

The story

Synopsis

Once close in their school days, Mizuto Irido and Yume Ayai unexpectedly become step siblings and must readjust to living under the same roof. Neither wants to be labeled the older sibling, so they establish a contest with clear boundaries: whoever breaks the rules loses, and the victor earns a single request. Their attempts to outmaneuver one another lead…