The Final Judgment

Trial of Power

Avoid the enemy's slow and preditable attacks. Keep attacking him until his HP is almost gone then stay away from him until the next cutscene.

Missable Trophy: Do nothing instead and let him kill you to unlock the trophy "Servitude"

Trial of Will

Repeat the process during the first trial and watch the next cutscene.

Trial of Resolve

You now have to choose whether you'll retreat or step forward. Keep slashing all the obstacles along the way as you move forth until the next cutscene.

Missable Trophy: Walk away instead of going forward to unlock "Peace"

Trial to End it All

For the quest's final phase, you'll have to fight Seneschal Savan and his main pawn. This is not particularly a hard battle so no further tactics is necessary. Your pawn will then grapple Savan and you have to finish the battle in a single strike. After landing the finishing blow, the quest will be complete.