Monster Musume no Iru Nichijou OVA

During a physical exam, Miia, Centorea, and Mero discover that they have gained too much weight due to Kimihito Kurusu's delicious cooking. To remedy this, Polt offers them first use of her new pool and gym facility before its grand opening. However, it's not all fun and games, as the three girls' competitive spirits start to flare up! Meanwhile, when Rachnera Arachnera receives a letter from her previous host family, she finds out that they would like to meet with her and apologize for the events that caused her transfer. But, as it turns out, not only do they want to apologize, they want her back as well! When the family's daughter, Ren Kunanzuki, shows up at the front door, the gang must convince her to let Rachnera stay at Kimihito's house. Bundled with the 11th and 12th volumes of the manga. The OAD adapted the manga's chapter 17 from the fourth volume, where Miia, Cerea, Mero, and Kurusu go to the gym's pool