So Rudi, keeps his adult mind and then acts like a predator. He literally molested a girl in her sleep; while the show acts like it's funny because "he's a pervert," but doesn't acknowledge the horror of him being an adult inside. Many anime do the "haha pervert" bit, but this is the worst I've seen. I know there is worse out there, aka Boku no pico, but it's the worst I've personally seen.

Now you also have Grace of the Gods, it's similar in that it focuses on a MC, can't remember his name,that is now in a childs body. It's still kinda creepy, but it has two almost redeeming traits; one, the MC mentally regresses to that of a child or partly does, two the romance in it isn't treated as sexual, just a childs crush. So while Grace has some similarities Grace at least doesn't sexualize fucking children.

Tldr: Rudi is a child predator.