Yuzu Aihara, a fashionable high school freshman, faces a sudden school transfer due to her mother's remarriage. Amidst her hopes for new friendships and romance, she clashes with the strict environment of an all-girls school. The attention-grabbing Yuzu catches the eye of Mei Aihara, the school's elegant student council president, leading to a surprising revelation—they are now stepsisters. Despite Yuzu's attempts at friendliness, Mei's aloof demeanor sparks tension, culminating in a startling kiss that leaves Yuzu bewildered. As Yuzu grapples with the aftermath, she delves into the enigmatic world of her enigmatic sister, questioning the true meaning behind their unexpected bond.