Recently, Shigure has been acing the swimming class, leading to Hamakaze getting depressed. Shigure reveals she’s been getting “private swimming lessons” from Admiral and Hamakaze decides to join her.
The thing is, "private lessons" are just an excuse for some kinky sex in swimsuits. Kinky sex is the reward for fast swimming. A pretty good teaching method, all in all.
By the end of this doujin, Hamakaze is acing her swimming too...