[Amuai Okashi Seisakusho (Labui)] Aku no Kagakusha, Mahou Shoujo ni Tenshoku Shimasu! [Shuten Doujin]

An evil scientist's career change comes with unexpected perks when a transformation leaves him as a busty new magical girl—complete with a cock that has a mind of its own. Strapped into his own laboratory's mechanical tentacles, the flustered researcher protests even as the machines wring moan after moan out of him, while his devoted horned familiar Grimoire watches and teases that Papa seems to be enjoying it. The real heat arrives when Grimoire pins her beloved Ichi-chan down and rides him through a shuddering climax, swearing she'll never let him go—forever and always.