Yui has a secret she's hiding from her husband: she's fallen into an affair with her son Tooru. She knows rationally that it's wrong, but she follows her uncontrollable instincts, deepening their relationship. At first, they only met secretly during her husband's business trips, but gradually the encounters increased, until she could no longer endure his absence. Now, rather than waiting for her husband to come home, she eagerly anticipates those stolen moments with Tooru, to the point where her husband's absence has become normal.