On the official website for the anime adaption of Monster Musume it has been stated that the 11th compiled volume of the manga series will be bundling a OAD DVD. The 11th volume will ship on November 12th 2016 and preorders for it must be placed before September 19th. Now regarding the OAD it will be adapting chapter 17 in the fourth volume where Mero, Miia, Kurusu and Cerea go to the gyms pool. The manga mind you originally started its release March 19th 2012 and has since then been ongoing publication. The series would later get an anime adaption which would start July 8th 2015 and ended September 23rd 2015 airing 12 episodes. Other spinoffs have been released as well for the manga and anime series. Finally is a plot summary for the series below quoted from MAL:
Monsters—they’re real, and they want to date us! Three years ago, the world learned that harpies, centaurs, catgirls, and all manners of fabulous creatures are not merely fiction; they are flesh and blood—not to mention scale, feather, horn, and fang. Thanks to the “Cultural Exchange Between Species Act,” these once-mythical creatures have assimilated into society, or at least, they’re trying.When a hapless human named Kurusu Kimihito is inducted as a “volunteer” into the government exchange program, his world is turned upside down. A snake-like lamia named Miia comes to live with him, and it is Kurusu’s job to take care of her and make sure she integrates into his everyday life. Unfortunately for Kurusu, Miia is undeniably sexy, and the law against interspecies breeding is very strict. Even worse, when a ravishing centaur girl and a flirtatious harpy move in, what’s a full-blooded young man with raging hormones to do?!