For me, 'That Time I Got Reincarnated as a Slime' stands out. The world-building and plot development are really engaging. Also, the characters have a lot of depth.
Well, it's a bit hard to pinpoint exactly which was the very first one. But some early examples could include 'El-Hazard: The Magnificent World', which had elements of the isekai genre.
Manga porn is basically adult-oriented manga that contains explicit sexual content. It's very different from regular manga, which can cover a wide range of genres and themes without that kind of explicit stuff.
Hentai manga isekai typically features outlandish settings and sexual content. The storylines can be quite unconventional and focus on fulfilling certain fantasies. However, it's important to note that such content may not be suitable for all audiences.
Isekai Quartet indeed has a manga. It offers a different perspective and sometimes delves deeper into the story compared to the anime. The manga can be a great companion to the animated version for fans wanting more of the Isekai Quartet world.
A hole in the wall porn manga often features graphic sexual scenes and may push boundaries in terms of vulgarity. Such content is often not suitable for public consumption and may have negative impacts on viewers' minds.