Here is my theory on why the idol wasn't in his class before: she probably had some kind of breakdown when she heard Yorumiya died without being able to make up with her, so she went to a different school.
To be fair I think she hasn't been relevant for a while. I think she last really showed up in chapter 36 which established that she works on Zagan's place.
Here's a Twitter thread with a little bit more info about the horse as well. From the thread I gotta note that in this picture if you check the smartphone you can see she is totally staring right at the viewer, and not the camera taking the selfie.
Artist drew them in bunny outfits because of japanese punnery. In Japanese, the numbers 8 (ba), and 2 (ni),) can be read together as “bani”≒“bunny”. This was posted on August (8th month) 2nd in japan time.
So a extra detail that WN states that this didn't: Remilla learned that if you take a soul and put it in an artificial body, it gains 100% perfect memory recall ability. So they'll always be able to remember everything exactly with no detail lost. Which is both a blessing and a curse. She tells...
Yeah really. Read this all just now and got hit by the cliff and went to check for translations, only to get hit by 'the story is going in a different direction.' Instead of joining school, he finds some weird indie company???