My Stepmom's Daughter Is My Ex

Step‑siblings, a rivalry, and a forbidden wish: can old flames survive the sibling shuffle?

Mizuto Irido is the quintessential underachiever, drifting through school with a head full of novels and a heart that never quite syncs with reality. Yume Ayai, his classmate‑turned‑first love, is the quiet bookworm whose world revolves around quiet corners and whispered verses. Their shared passion for literature sparks a tender middle‑school romance, but as they graduate, their personalities diverge and they part ways, each convinced the other was a fleeting chapter. Fate, however, loves a good twist. A remarriage throws Mizuto and Yume into the same roof as step‑siblings, forcing them to navigate a bizarre new hierarchy. Neither wants to be labeled the “older” sibling, and their stubborn pride morphs into a petty competition: whoever crosses the line of sibling etiquette first loses, and the victor earns the title and a single wish. Living together, old memories flicker like marginalia in a well‑read book, and the thin veneer of rivalry begins to crack. As they spar over trivial rules and shared chores, suppressed feelings resurface, turning everyday banter into a delicate dance between sibling rivalry and lingering romance. The series rides this awkward tightrope, blending snappy humor with moments of genuine heartache, as the duo wrestles with the question—can a love that once was ever truly be rewritten?

A rom-com about exes forced to live as step-siblings who engage in a competitive game to suppress their lingering feelings. Expect moderate fan service and a premise built on pseudo-incest tension that may discomfort viewers sensitive to step-sibling romance tropes.