Grima Build

-def is kinda sucky, but the HP bane in turn give him more bulk. I got a +Hp -speed one, and I run Fury, Vengeful Fighter, and Armor march. You can run the same thing, with the C skill being anything you want, from Ward Armor, Ward Dragons, or Armor March. He should also run Aether to make back the Fury health and its runnable since he has a fighter skill.

If you're planning on using him long-term and maybe merging into a better IV, you could go for wary fighter+ breath skill + glimmer. The extra HP makes hard to knock him out of wary fighter in one hit, so he will likely survive at least two rounds.

One relatively direct way to exploit his HP if you have an extra Boey is give him earth boost.

Other not-too-conventional ideas, both of which exploit his massive atk stat and targeting the lower defensive stat of most units to avoid needing additional damage from specials
- if you're ok with sacrificing a Y.Ike, pavise + heavy blade + vantage + deflect melee. I think I posted this build a while back; you can look through my profile if you want to dig it up. The idea is to initiate, let pavise absorb the first hit, and deflect melee absorb the second while giving him 1 special charge. Now he's in vantage range, so whether on player or enemy phase, he hits first, gains two charges thanks to heavy blade, and pavise is active and we repeat the process. Percentage-based reduction scales well with lower def and more HP, so your IV is actually relatively good in this build.
- wary fighter + brazen def/res + noontime or sol (probably sol). Get his defenses up into the upper 30s and keep healing up to maintain wary fighter.
- bold fighter + escutcheon: similar idea as the first. Or just bold fighter + bonfire, just forget about his defenses and attack