Hikaru, the stepdaughter of his new spouse, joins the household, and life settles into a peaceful rhythm for Dad. But this tranquility doesn't last long. Hikaru gradually begins acting out—behaving dutifully in front of Mom, yet secretly seducing Dad. As a man experiencing fatherhood for the first time, he finds himself helpless and bewildered by her advances. Then, on his birthday, the gift Hikaru gives him delivers a shocking revelation that shakes him to his core.