I'm not a lawyer and I don't know much about these things, but I believe these would be considered parodies, which fall under Fair Use. In general from what I've seen, as long as your adult parody is not tarnishing the reputation and doesn't mess with the profits of the original work, the companies don't really care and seem to be pretty lenient when it comes to 2D art.
It's different with 3D characters, however, especially if you use models exported from the original game.
I think that's why certain hentai sites changed certain words like "Overwatch" to "Overlook" or something else. Blizzard really didn't want anyone making 3D porn of their characters.They realized fighting this is futile and just kind of gave up after a while.
Companies have realized there's basically no point in fighting adult parodies. A waste of time and money, and cease and desist letters and threats of suing are not going to stop the guy who lives in a third world country from drawing smut of your work. They're just going to change names and continue as usual.