Nephenee

+Atk -HP is really good. Her build is pretty straightforward. She come with Wrath, one of the strongest B skills in the game.

A: Fury or Brazen Atk/Def
B: Wrath
C: Flexible
Seal: Spd Smoke? Drive?

For her weapon, the Dauntless Lance now gives you effective against armor. The refine is a toss up. Since yours is +Atk I would probably go with the +Spd refine for both phases rather than the Spd/Def stance effect on enemy phase only.

I can see your concern. +Atk is good, but then -HP kills her already-mediocre HP (as a unit that's supposed to tank, no less). My ideal with fast and tanky characters is to make them as fast and tanky as possible mixed in with Atk Smoke so they can survive a lot longer. The problem is, one of the Spd/Def A-slots is either Fury (kills her tanking HP) and Spd/Def or Steady Blow (premium skills)... what you can do is maybe make the best of her +Atk and have her maximise on charged Moonbows since her refine gives it 1-turn cooldown charged every round once Wrath kicks in (on top of Armour effectiveness).

Alternively, below is my take on trying for a mixed phase approach. If you just care about her Enemy Phase, Close Def (or Steady for premium) really work. Her Spd/Def Stance effect works on Enemy Phase.

My neph