Kenji's sister-in-law Mai comes to check on him, worried about him as his wife returns to her hometown to give birth. Kenji likes Mai's cute smile and welcomes her back, overjoyed to see her again after such a long time. However, Mai's real goal, as her relationship with her husband is not going well, is to release her sexual frustrations on Kenji. Unaware of this, Kenji is soaking in the bathtub when Mai sneaks up on him...