While Erika, Kyouya, Sanda and Kamiya are talking about their plans for their upcoming summer vacation, their conversation switched to Kyouya’s mom who lives in Kobe. As they are walking, the four of them sees a guy trying to hit on a woman but he gets terribly rejected by her somewhat intimidating way of speaking. It turns out that she is the older sister of Kyouya, who seems totally dumbfounded seeing his sister with her baggage. Erika nervously introduces herself to Reika Sata as Kyouya’s girlfriend. Right after the brief introduction, Reika drags her younger brother home where she will stay for the meantime. She asks him about Erika and thinks that he is not serious about her so she tells him to just break up with her. However, Kyouya implies that his decision to be in a relationship with her is not done on a whim, which leaves his sister surprised.
The following day, Reika invites Erika out on a date as they eat various desserts, which makes the latter feel full. But for the sake of good impression, she tries to take another bite when suddenly, two guys arrive and hit on them. Reika perfectly shoos them away by telling them to go to the zoo and flirt with the female monkeys instead (LOL). The men get scared and they immediately go away. Reika complains to Erika about how men tend to flirt halfheartedly at girls and treat them like fools. She also doesn’t believe how her brother suddenly changes, and calls him a boy who’s not worthy to be called a man, just like most guys. Erika objects and begins to argue with her, telling her that Kyouya can also fall in love with someone seriously in contrast to how Reika describes him. To end the argument, they both agree to do a challenge and if Erika wins, Reika will apologize to her.
Meanwhile, Kyouya is at Takeru’s house since he doesn’t want to be in the same roof with his sister. He complains about how she loves to order him around and bully him ever since they were kids. Right then, his phone rings but he doesn’t want to answer his sister’s call. Takeru persuades him to get the phone because he might just get into trouble later if he doesn’t answer it. Reika tells him on the other line to go to Glouton Hotel as soon as possible, but when he refuses, she tells him that something bad might happen to his girlfriend if he doesn’t come over quickly. Sensing that Erika might be in danger, Kyouya immediately goes to the venue and sees his sister waiting for him. He looks for Erika but she tries to stop him, which makes him upset, surprising his own sister with the sudden change in his behavior. Just when he is about to continue walking, he hears Erika puking in the bathroom. Apparently, the two of them decided to have an eating contest in a dessert buffet restaurant so she ended up consuming more than what she could handle. After slapping her brother for embarrassing Erika, she goes to pay for their bills as she thinks about what he said earlier.
On their way home, Reika tells Kyouya that she wants to bring Erika to Kobe to introduce her to their mom since she has already taking a liking to her. The three of them travel to Kobe right away to meet her, and while waiting for her to arrive, Erika feels jittery. While Reika tries to comfort her, her mother finally arrives, and a short-haired, muscular woman appears in front of them, much to Erika’s surprise.