Alm build suggestions

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Draconic Aura/Aether (budget/optimal)
Death Blow, Renewal (or Windsweep), Threaten Atk/Def.

Mine has Renewal and Threaten Atk and I love it. :) and I don’t have Aether fodder for him yet, so I still have DA on him.

Pseudo-healing Alm is great.

Refine his Falchion to get the Double Lion effect(the effect that turns it into a Brave Sword, you probably already knew this but I mention it just in case)and give him Death Blow and Moonbow/Glimmer. Then as your B skill you can use Renewal, Windsweep, even Quick Riposte to give him some enemy phase presence, or Cancel Affinity in case you want him to duel TA Nowi and Corrin. C skill is flexible, but after the refine even with -HP he reaches 45 HP so you can go for Infantry Pulse, for example(same HP as Dorcas, one of the few units that comes with the skill by default). Threaten Defense is also a great option to give him even more firepower. Those are some examples, anything can work here.

Your sacred seal should probably be either Phantom Speed or Heavy Blade. Phantom Speed helps you activate Windsweep against more units, while Heavy Blade will allow you to proc Moonbow/Glimmer consistently. If you want him to tank melees Close Defense can work as well. You can also give him +Attack or something along those lines. If you don’t use Heavy Blade you can use a higher cooldown special like Luna.