Armored unit delema. I need another set of opinions

I just got Halloween Kagero from my free summon on the Mythic banner. So, should I merge her with my current Kagero (+ATK/-HP) or fodder her to H!Myrrh or Idunn for Brave Fighter?

Can I see the current builds for all 3 units? Because it depends on how Bold Fighter will be used. (All 3 units can be posted in one go)

I would say save it for a unit who can use the skill to it’s full effect. H!Myrrh has her weapon for player phase follow up attacks, and Idunn is better as an enemy phase tank. The armoured ranged units are the best users of these skills. LA!Lyn is a notable great user because Juicy Wave+ can let her make gauranteed doubles without the foe counterattacking. Pair this with glimmer/Moonbow and it can be a deadly combination.