This Seeking Tech guide will show you how to get the Divine Intervention trophy in Jeanne d’Arc. To unlock this, all five Armlet Wielders in your party need to transform into their Holy Armor in the same turn order.
This can be done after the 34th stage of the campaign. Afterwards, you can try for this trophy in the final two stages of the story, or wait until the post-game.
If you decided to wait until the post-game, I recommend that you look for a Free Combat stage where the enemies won’t bother you, like the Altois Prairie.
From there, wait two turns. On your third turn, you should be able to transform all five Armlet Wielders at the same time to unlock this trophy.