Kei, a married woman and stay-at-home mom, wed a man with a son from a previous relationship. Her stepson, Makoto, witnessed his biological mother's infidelity as a child and developed deep distrust toward women. He keeps his distance from Kei, refusing to open up to her. One day, Kei discovers Makoto secretly washing his pants after a nocturnal emission. She gently reassures him, telling him it's perfectly normal for a healthy boy and nothing to be ashamed of, then carefully washes his penis with tender care. Wanting to help Makoto overcome his emotional barriers and develop a healthier understanding of women and sexuality, Kei decides to use her own body to provide him with intimate sex education. With warmth and boldness, she embarks on a journey to bring light into his heart, guiding him through explicit lessons in affection and desire.