Toumei Ningen (OVA)

On his way home from his dead end job as a convenience store, Mie accidentally knocks into an unusual man in a hat who happens to drop a weird medicine as they knock into each other. When he takes the medicine, he finds out that the medicine can make him invisible. Mie soon takes advantage of this new ability by going to peep and molest at a public bath, a classroom, and one of his work colleagues that he doesn't get along with.

The term "Invisible Stud" is a little bit of a stretch for the main character, since he's more like an "Invisible Horny Stalker", ... "Invisible Horny Loser", and "Invisible Horny Molester" all combined. I don't even know how much of a stud you could if you had to molest your way into a situation with a medicine that prevents people from knowing who you are by making you invisible, but that's all semantic stuff that really doesn't matter too much since it's a porn we're dealing with here.

Most of the sex scenes are pretty meh, but there is one decent sex scene, and that's definitely the one set in the schoolroom, and that's because it's 80% hot, and 20% actually funny. It's a shame that the rest of them aren't as memorable, since the premise had enough potential to have a few more interesting sex scenes. The comedy is OK, but nothing to write home about. Once you watch it, you've got the gist, and would probably skip it on a second watch.

The second series "The Invisible Stud Returns", is where all of the better jokes are, since the concept has already been set up in the first one, so the second one manages to go a bit more in-depth and interesting with the concept and situations for it's sex scenes. There was even a joke from the second series that managed to get a laugh out of me. None of the sex scenes quite reach the heights of the schoolroom one from the first, but overall the sex scenes are a lot more enjoyable.

Overall, The Invisible Stud is worth checking out for that one sex scene and not much else, and the sequel is worth it more for the comedy and plot if for some reason you're into having that in your hentai. You could do a lot worse on both counts. I know that's not a ringing endorsement, but not every hentai can be a shining diamond.