Shou-chan's father brings his mother-in-law, Ryumiko Yanagi, over for the first time in several years. Shou-chan is excited by his mother-in-law's big boobs! His mother-in-law, worried about Shota, who has been feeling down lately, visits him to find out the reason, and to her surprise, he says that he is "worried about his mother-in-law's big breasts...". Despite his mother-in-law's worries, Shota takes this as a great opportunity to touch Rui's big breasts and plays all sorts of pranks on them! He wants to bury his face in her big boobs, so he challenges her to play, tries to take a bath with her, and plays all sorts of pranks on his busty mother!