Octopath Traveler 2 - Shadowy Boy

In Gravell, we discovered the boy with the cursed teddy bear, but I couldn't figure out what we were supposed to do. After putting way too much effort into this, we find the boy at sunrise outside town and the only person who can interact with him is Temenos, for a special battle. Usually we are conducting an inquisition, but today, we are performing an exorcism...

The reward for this is a staff that serves as the ultimate weapon for an Arcanist, boosting both light and dark. It can serve as a decent weapon for Temenos by boosting his light spells, but I prefer to give him something else.