Part 1 The Minami sisters decide to take a trip to the beach on the upcoming Sunday. But with their bathing suits being too small, Chiaki and Kana go off to get bathing suits with the two settling to get bikinis. The two pick out a revealing two-piece bikini for Haruka so she wouldn't stand out. However, Haruka gets rather uneasy with what her sisters buy for her.
Part 2 It is raining heavily and Kana frets over the rain making it so the beach trip would have to be put off it doesn't stop. To stop the rain, Kana decides to make a teruterubouzu (paper doll made by children to stop rainfall). But instead of making one of paper, Kana makes a human-sized one out of Chiaki by wrapping a sheet around her and tying her to one of the clothes-drying racks in the house. Now Chiaki has to negotitate with "Raincloud-san" to bring about clear skies so she can get out of her predicament.
Part 3 The Minami sisters and Chiaki's friends arrive at the beach, but Haruka is embarassed to unveil her revealing bikini that Chiaki and Kana got her. The two younger sisters try to get Haruka to take off the shirt covering up her bikini.
Part 4 While Haruka and Chiaki's friends go off to get drinks, Kana talks to Chiaki about her worth to her youngest sister which get the two into one of their usual silly arguments.
Part 5 The Minami sisters return home from their beach trip with a serious tan and receive phone calls from Chiaki's friends who tagged along for the trip. In both instances, Kana answers the phone where the topic is about their sunburns, Kana lying about serious problems with the sunburns, Kana getting whopped by Chiaki to take the phone saying it was a lie, and the friend talking about how different each of the sisters were.