Forced to live in his stepmother's home after his father's remarriage, the boy found himself sharing a house with her daughter—Yuna Hinata, five years his junior. Yuna had become a shut-in after suffering severe bullying at school, leaving the family at a loss. Feeling sympathy for her, he patiently reached out, gradually breaking through her walls. As their bond deepened, it crossed the boundaries of siblinghood. Yuna began to develop an intense emotional dependence on him, eventually seeking a sexual relationship. Their forbidden connection grows stronger, weaving a complex tale of twisted affection and undeniable desire.