Take a Fighter as Leader and be sure he have the skill "Guard" equipped. He knows it with Lvl 1.
Then go to Quests, pick the Travel Quest "Search Resonail" and take Ruinsholt.
Search an enemy and let your Leader die, then finish the fight. After the fight your Leader lives with 1 HP, search and fight another enemy and walk with your Fighter (Leader) as far away from enemy as possible and use the skill "Guard" to have a shield. Then finish the fight with the other character and you get the Trophy.