Creature Girls: A Hands-On Field Journal in Another World Vol. 9 (manga)

While Daisuke Kurimusubi wants to be the king of a monster-girl harem, his old friend and fellow earthling Taishi Oritsue has become something closer to a Demon Lord. Between rounds of carnal debauchery, Oritsue has overcome even the mighty basilisk and begun innovating on all sorts of unorthodox inventions. What's more, the maids who once looked down upon him now desperately wish to bear his children. The nation under Oritsue's control grows more powerful by the day! And out at the centaur village, Daisuke's quality time with Nea is interrupted by the emergence of a mysterious "headless woman" from out of the darkness...