Recently, Sumire's husband has been suffering from erectile dysfunction, so she has been trying to ease her frustration by exercising. One day, she notices her son-in-law, Shinya, secretly spying on her while masturbating... Sumire can't stop thinking about his huge cock, which she happens to see, and she secretly helps him ejaculate, day and night, under the pretext of helping him release his massive penis, which is too big for her to hold in her hand. The son-in-law is driven crazy by his mother-in-law's service, which she offers 24/7, wherever she goes...