This is an unmissable, story related trophy. Because it's meant to be a secret trophy, I'll put its translation and such in spoiler tags.
*** Spoiler - click to reveal ***TROPHY NAME -------------------- Journey's End
TROPHY DESCRIPTION ----- Defeated Krom
Krom is.. A doable, but slightly annoying fight. He doesn't seem to have any specific weaknesses, nor is he resistant to anything, which means it'll be a battle of using whatever elements you want.
One important thing to take note of, is when you get his health down low enough, (about 4k damage worth) he'll use a skill that heals all damage done to him. This is a one time heal, fortunately, so just think of anything before so being a mock-period of testing what works out against him.
There are many setups and strategies and spritnites out there, so telling you to stick to a single one (considering you've probably got your own) would be useless. Though, some helpful advice is nice, so;
If you use Sherra, take note she can get spritnite that allows her to X Heal, which heals everyone in battle for an insane amount. She also has Symphonia, which gives everyone one momentum charge, helping you prepare some harder attacks.
If you have a momentum spritnite for any kind of magical resistance down, use that on him, then follow up with said magical element to do harder hits. For example, I used fire resistance down, used a skill from Galdara that lowered his defence, then used Obaro to hit with a powerful flame attack. Hitting him for well over 1k.
It's a matter of endurance for the most part, the boss hits hard, but you can heal more if you keep on point. If you used X Heal, and need more heals. Kanata should have Aura, or you could dedicate two party members to using potions, as the other two continue to damage him. His strongest attack will take 2-3 hits to fully deplete your party if you're 47+, so it's not like he can one hit you.
He does one move where he'll fly in the air, damaging you as you take off. Use this 1turn period to heal and ready up, as he'll come swooping down damaging for the same number as he took off. Meaning nothing changed, but your party members at least have more HP than what they would have.
IMPORTANT: Like most bosses from these developers, once you fully deplete his health, he'll send out an AoE attack, hitting all allies. If you can see his health bar due to the Artifact, then make sure everyone has 250+ HP to survive it.
Hope some of my advice helps. Like I said, everyone has their own setup/party. Good luck!