The affluent and happy Goto family. The bonds of family are now about to turn into a forbidden relationship. On the eve of Suzu, the third-generation Kamezosuke's remarriage and her birthday, Kamezosuke has one son, while Suzu has two step-sisters. The entire family planned a commemorative photo shoot for her birthday, but by the next day, the photo session ends and the parents go out for dinner. Seizing the opportunity, sister Reira begins plotting something in front of her stepbrother Manabu. The moment the family's bonds begin to unravel is drawing near.