General Alma
At the start of the battle, he’ll be entirely invincible. You can still let your attackers keep him busy and take control of Miki if you want to take care of the healing. You can’t do anything for now so just let the battle go on while healing your damaged party members until a cutscene plays.
Once Alma’s shields have been neutralized, throw everything you have at him. He’s considered a humanoid-type enemy so the Warrior Slayer role will work wonders when equipped to one of your melee fighters. He has strong melee attacks but he also has a projectile attack that he can use to interrupt your ranged characters. It’s possible to stagger him in a barrage of continuous attacks. Once his HP drops to 50%, another short cutscene will trigger.
This time, Alma will utilize “signet replication”, his body now filled with signets. And as expected, the next phase of this battle will commence. He’ll have a powerful area-of-effect counter skill called Bosom Blow that can knock down anyone around him, with a good chance of getting stunned as well. It’s imperative that you keep Miki out of the way since her healing will be your party’s lifeline in this battle.
His main attack skill is Ground Wave, a powerful melee move that can deal heavy damage to anyone near him in a wide-angle attack. Fortunately, he doesn’t seem to change targets much often so if you keep pummeling away with your fighters, your ranged characters are pretty much safe from harm as long as you keep a good distance. It’s still possible to stun him in this form. When his HP drops to 25%, another cutscene will trigger.
Transmogrified Alma
Similar to his human form, this battle starts with Alma having a barrier making him invincible against any kind of attacks. Also, you want to replace the Warrior Slayer role equipped to your character to the God Slayer role (if you have it unlocked already) since it will help a lot in this battle. Furthermore, Alma gains a ranged attack called Seraphic Rebuke which deals multi-hit damage while also silencing the target. He will use it effectively against your ranged characters so make sure to either equip Miki with an Anti-Silence Amulet or use Chamomile as soon as you can since you’ll need her constant healing in this battle.
As the battle drags on, Alma will unleash a massive shockwave that will instantly defeat your party. There’s nothing you can do to prevent this. A cutscene will follow afterward.
Spoiler:
After the scene, Alma’s barrier will be disabled once again. At the start of the battle, cast Fiore’s Sacred Pain to lower his elemental resistances then fire away with your most powerful attacks. If you see him buff himself, immediately manually cast Fiore’s Void skill. He still retains his powerful Bosom Blow counter that can damage and stun but it’s now limited to anyone in front of him. Alma also has powerful AoE attacks but you’ll have no choice but to soak up the damage and heal. At this point, Miki should have access to Faerie Star so use that manually if you have to; just make sure to prioritize using group heals instead of individual heals. You can also activate your Reserve Rush near the end of the battle to have a very fitting finish.