At age 20, Hitomi met a man who was already married with children, and became pregnant with his son, Tatsuya. However, the man strongly urged her to have an abortion, so Hitomi disappeared from his sight and raised Tatsuya alone. Their relationship was less like mother and son and more like close friends, and as Tatsuya grew, he increasingly resembled his biological father. Watching him mature, Hitomi found her old feelings reigniting. When Tatsuya reached school age, the two finally crossed the line into a sexual relationship. Now, as Tatsuya turns 20, Hitomi plans a hot spring trip with him to celebrate their special bond and mark this intimate milestone together.