How to Complete A Lost Companion
You only have to defeat Gade to complete this quest. It is against the law to inflict debuffs in this battle (but receiving debuffs is not against the law).
Gade is an undead unit, so he can be damaged with healing spells, potions, Phoenix Downs, and Holy attacks, in addition to standard weapon attacks. He absorbs Dark attacks, so don't equip Dark weapons or use Dark magick attacks for this battle.
Gade and the other undead enemies will become gravestones when they reach 0 HP, and they will come back to "life" after three turns. The gravestones can be permanently removed with a Phoenix Down, the Raise or Arise spell, and other moves such as Exorcise and Burial.
When you complete this quest, you get a knife called Tiptaptwo, which teaches Adelle the Heritor ability Viola.