Aiko desperately resists her son's desire for her body. She tries to persuade her not to let her son enter this forbidden world, but he doesn't listen and keeps forcing himself on her. Unable to resist the strength of her grown-up son, Aiko gives up and decides to accept her son, setting a rule that "if it's just the tip, it doesn't count as sex." Connected only by the glans, the two are engrossed in a play that is one step away from the forbidden world. However, Aiko finds that she can no longer be satisfied with just the tip before her son does...