1年前、再婚でやってきた綺麗で優しい母、れい子。新しい家庭は夫と大学生の義理の息子、友真との3人暮らし。和室でオナニーをしているれい子。息子・友真は廊下を歩いていて、偶然その光景を見てしまう。夕食のとき、友真は、意を決して母のオナニーを見てしまったことを言い、その事でれい子のことが気になって何も手がつかないと怒り出す。夫とのSEXの後、れい子は息子のことが気になり、友真の部屋へ入る。いきなり抱きつき求めてくる息子・友真。れい子は戸惑いながらも、そんな息子とのSEXを受け入れてしまう・・・One year ago, Reiko, a beautiful and kind mother, came to Japan after remarrying. Her new family consists of her husband and her college student son-in-law, Tomoma. Reiko is masturbating in her Japanese-style room. Her son, Tomoma, is walking down the hallway and happens to see the scene. At dinner, Tomoma tells him that he watched his mother masturbate without meaning to, and he gets angry because he can't do anything because he is worried about Reiko. After having sex with her husband, Reiko is worried about her son and goes into Tomoma's room. Her son, Tomoma, suddenly hugs her and asks for her hand. Reiko is confused, but she accepts to have sex with her son...