The Security Corp will need help investigating the rumors of a Drifloon interacting with the local children.
The Request
Check on the chalkboard in Galaxy Hall to accept this request.
Talk to Miki
Miki is near the southern gate of the village. Talk to her.
Visit Prelude Beach in the Evening
Prelude Beach is where you first arrived in the Hisui Region, south of the Practice Field in Jubilife Village. Use the bed in your quarters to rest until evening (If it's the wrong time of day, the guidance marker for this request won't be there), then go to the Practice Field and go west to reach Prelude Beach. Check behind the hut by the beach, and there will be a cutscene.
Report to Miki
Go back to Miki near the south gate of the village and talk to her.
Reward
Afterward, you get 1 Stardust.