Thoughts on F! Kana build and advice for C slot skill?
Pretty similar to my build, but I'd go Aether, QR, Atk Smoke, and Close Def seal. Stacking Water Breath with Close Def and a Breath skill is absolutely broken; my Kana just about walls every non-red melee unit except B!Ephraim, so it can be a pretty solid idea.
QR is cause her spd is high, but not really high enough that I'd see her doubling all the time, which you'd probably want.