Shoowa, raised in a single-parent household, finds his life changing this summer when his father, Noboru, remarries his father's young and attractive subordinate, Honoka Tsujii. Perfectly matching Shoowa's ideal type, Honoka gradually stirs his emotions day by day. To celebrate the remarriage, they plan a trip to a local hot spring inn. However, Noboru is suddenly called away for work, leaving the two alone. Seizing the opportunity, Shoowa and Honoka begin a forbidden relationship in a secret room. As passionate desire blooms between them, a deep bond forms that transcends the boundaries of family—how will this intense connection culminate by the end of their journey?