F!Corrin's B-skill

I've been wanting to build a F!Corrin built strictly as a defensive wall/debuffer.

So far I have:
+Spd, -Res
Dark Breath, Def refine
Bonfignis
A - Brazen Atk/Def, at least for now
B - ???
C - Some support skill like a Tactic (Res maybe?)

Guard and Wrath stand out as options, but I'm not sure if it's worth foddering my spare Karla to her if she'd prefer another B skill. Any suggestions?