Koi's son, Masaru, has started coming to peek at Koi's bath when her husband is away on a business trip. Koi invites Masaru to join her in the bath. Masaru enters the bath happy but shy, but his crotch is already rock hard. Koi is surprised, but unable to bear to see Masaru flustered, she decides to calm him down by taking his hot cock into her mouth...