It’s quite natural to set a teen romance like Kinkyori Renai (近キョリ恋愛) in the summer. First of all, there’s summer vacation, which the class celebrates at the start of this episode:
Well, all except for Haruka (Abe Aran), who seems a bit less enthusiastic. He and Mirei (Ishibashi Anna) are both concerned about Ririko (Adachi Rika), who is planning to go back to New York, but hasn’t managed to tell her two-timing boyfriend Tachibana (Nagayama Takashi) that.
The second reason is, of course, the obligatory beach scene (or scenes). Kanata (Kishi Yuta) is the one who proposes the beach party in this series, but it was bound to happen somehow. He also wants to make it a farewell party for Ririko, but it sounds like that’s just a plot from the basketball team to get Ririko to the beach.