Ten years ago, emiko sugioka divorced her husband and raised tatsuya alone. Tatsuya also secured a job and will move out in April. One day, tatsuya invites her on a graduation trip to a hot spring. "Mom, thank you. I've always loved you..." Emiko's heart wavers with tatsuya's sudden confession. She couldn't bear the thought of living apart after this trip. Sweet air flows as the real mother and son open the forbidden door...