that's guest content, Hyao can't control how fast that gets made.
oh, that's a crossover character, guest characters are people that write scenes for the characters that Hyao added in for them. I'm uncertain if they are his friends or just people who paid more on patreon or something but on the guests' characters they are
1. Scrap
2. Hayden
3. Ste
4. Arion
5. Xer
that's all of them I think, excluding Nauxus but that's cause again he is a crossover character, the difference being that Guest characters come back and are writing by someone else, while Crossover is only once. I am mostly assuming that difference since we have only had one crossover lmfao.
I think a better description would be that crossover characters are part of a different media, in this case another bara game on itchio (Tavern of Spears was it?),
(while guest characters are still from the same source, Lustful Desires, but written by guests authors and indeed implented by Hyao in the game.)