Briella is as likeable or as unlikeable as you want her to be :P
On a serious note, I did find it challenging to give Briella consistent characterization, or even any characterization at all, as she's under your control for most of the game. This is something that's frequently brought up as a feature, problem, or challenge with western RPGs and it's something I'd like to improve on in future games.
You didn't mention the name of the anime, but you did mention the verse in passing and you did mention the "Winter 2020 anime adaptation" as well as dropping one of the themes as a hint. It wasn't hard to figure out from there where the secret themes came from and the public ones as well once I had that information.