Reach Relationship Level 6 with Monoco. Progress the story around Act III and choose to spend time with him back at camp. You must complete his side quest, which is to accompany him to the Sacred River to resurrect Noco. Head to the Sacred River > Fight Golgra > Resurrect Noco > return to Camp. Requires Esquie's ability to fly to reach the location
Level 6 relationship + side quest: Sacred River → fight Golgra → resurrect Noco → return to camp. Requires fly ability.
Information sourced from community resources