For anyone confused like me, looking at this on the artist’s Pixiv shows that the Star Sapphire-looking character is Kaguya’s VTuber rig thingy. Kaguya’s the one who said insulting things on stream, it is not her being angry at people forgiving Star Sapphire for that.

EDIT: Failed to realize this was posted 16 days ago, leaving this here for anyone coming across it browsing.