To begin the 13. The History of Stahl in Trinity Trigger, speak with Ionia in the Stahl Kingdom: Cemetery. For this quest, you’ll need to defeat 3 Treants, which can be found in the Stahl Plains: South.
After defeating the Treants, return to Ionia to find out that a girl has been kidnapped. Return to Stahl Plains: South and make your way to the objective in the north. Once you approach the open plain, a cutscene will trigger followed by a fight against 3 Treants.
Take them all out to complete the quest. As a reward, you’ll receive an Intermediate Medicine and Mature Trinis Herb x6.