How can I build my Micaiah?

I think she's fine, but if you think she doesn't do enough damage you can just change her bond skill to Death Blow, but I'd keep the bond skill personally. Also I'd maybe use Iceberg instead of Glacies, since Iceberg will charge faster and she won't be doubling a lot of units with 20 Spd.

HS Micaiah's base kit can work pretty well to be honest. I personally run her with her base weapon and dance, along with Iceberg. But since yours is plus res, you could keep glacies if you can wait for it. For A, you could run death blow because of her high attack, or keep Atk/Res bond if she's going to be closer to her teammates. For her B, Fireflood dance works, or you could do Wings of Mercy. Chills also work. For her C and S you could run any ploys you want. (I run her Res Ploy and Atk ploy.) Hope this helps!