♥

♥

♥

♥

♥

♥

♥

Challenge: Can you find this secret about Koishi?🎔

While getting my 100 Perfect Clears of Koishi's Extra Stage, I happened to notice something odd during her boss battle. Looking online and even searching with an image yielded no results, so it seems like I'm the only person who knows about this secret. I desperately want to talk about it since I feel it's very significant for her character, but then I thought...why not make a challenge out of it?
If you're unfamiliar with Touhou or lack access to the games, that's okay! You do not need to actually play the game in question to succeed in this challenge. You can watch any Youtube video, or any one of my replays, and find the "secret" there.

Criteria🎔

Below is a list of criteria for defining this secret. If you think you know what it is that I'm talking about, try getting in contact with me and I'll draw you something for free if you get it right! (Anything SFW within reasonable limitations.) The best way to do this is through my email that you can find at the About page.
It is entirely visual. There are no audio components.
It happens only once during the Extra Stage of Subterranean Animism.
It happens multiple times during another section of the game.
Be careful using tools like thprac to find this secret. There is a glitch involving thprac where it will skip the secret.