The pool episode you've been waiting for actually lands the comedy instead of just coasting on fanservice. Miia, Cerea, and Mero in one confined space means character friction you don't get in the main series, where everyone's too busy orbiting the protagonist. It's lighter than the TV show and thinner on plot, but if you're already invested in these dynamics, this is exactly what you wanted, the girls actually reacting to each other instead of just existing in the same house.

It is physical exam day for the monster girls living with Kimihito Kurusu, and the results are mixed. Coordinator Smith points out that Miia, Centorea and Mero have put on too much weight thanks to Kimihito's tasty cooking. To help them slim down, Polt lets the three try out her new pool and gym before it opens to the public, but their rivalry soon heats up. Meanwhile, the arachne Rachnera receives a letter from her former host family, who want to meet her and apologize for what led to her transfer. They also hope to take her back, and when their daughter, Ren Kunanzuki, arrives at the door, the household has to persuade her to let Rachnera stay. This two-episode OVA is a comedy fantasy romance with ecchi elements, released with the eleventh and twelfth volumes of the manga.