As I know unity offers a free license as long as you show their logo on startup so this is not a problem.

However, it is pretty dumb to make pure guru game which has no other content at all. it should still have some kind of story and some logic to make it fun to play. it can even be a piece of art if you incorporate guro into some kind of narrative where for example the main character has schizophrenia

Also Guro content is insanely hard to produce unlike plain stuff or even plain porn because you need to manipulate your character models a lot and all those manipulations have to be procedural and cannot be even scripted or else it will be boring.

Even if you make some half playable guro game selling it will be problematic, because not that many people buy games and paying for something that is not even good enough makes no sense

we already have one guy here who is trying to make most decent guro game so far but he did not move very far.