They are cat demi-humans and monster in the tensura verse. There some main side characters show from the verse anime, manga, light novels, and web novels of the tensura verse. Also, there are others that can be found in the lore of the tensura verse.

Luminous is the only person able to see the reincarnated for Luna because Luminous is her mother. I will explain more about the reason why see can see that title in a future chapter.

Yes they are racial skills

It is the abbreviation for "So What I Got Reincarnated As A Spider" anime/manga.