Masato, his stepson, was dumped harshly by his girlfriend. Feeling sorry for Masato, who masturbates to ease his loneliness without a girlfriend, his mother Saori makes a suggestion. "I'll even let you do some bare-kneed sex with me." Masato can't believe what he's hearing, but he can't turn down Saori's kindness and accepts her unusual suggestion. His private parts get wetter every time they do a bare-knee sex, and his desire begins to rise up...he starts to move his hips so that they intentionally hit her clitoris!