Well, while they weren't isekai'd themselves (no, not even Stunk, though it's possible Stunk's father was an isekai protagonist, considering he has a harem), the fact people being isekai'd to their world is a common thing might make it eligible for inclusion, especially since Kadokawa owns the license for it.

- First question, everyone: who here would like to be steamboated by a penguin?
- … What.
- Haha, just joking, just joking. Let's be real, penguins are not frankly sexy.
- Oh thank Gods.
- Zombis, on the other hand…