Setsuna isn't one to let tyranny like this go through. She's dealt with world-ending stuff before, what's one megalomaniacal ice queen?

For anyone wanting to group up, she does specialize in extermination of monsters/spirits/etc. while being a skilled swordswoman, so she'd be good at fighting and storming the castle.

Just don't expect her to win against Winter after that if she ends up fighting all the way to the Queen. SHe's good, but she isn't Negi.

She can also do the stealth route, and damn I didn't mean for this to be so long.