After losing her husband and raising her son alone, the mother finally sees her child graduate and secure a job. As a graduation celebration, the son makes a move on his mother. At first she takes it as a joke, but ultimately they end up sharing an intimate relationship—just for that one night. Soon after, the son is transferred to a distant workplace, so the two decide to go on an onsen trip together to celebrate. During their journey, the son once again desires his mother's body. Amid the misty hot springs, the forbidden love between mother and son begins to blossom, leading to passionate encounters again and again. Though they know this is wrong… the seriousness in her son's eyes shakes the mother's heart. They lick each other's intimate areas, tongues intertwining as their taboo bond deepens. Beneath the warm waters, the connection between mother and son grows stronger than ever.