Reference article
Beach Clean Up
Collect the paper cranes from the beach before the rising tide reaches them.
Guide
Run into each paper crane to collect it. Start with the low-lying cranes nearest the water, then move uphill as the tide rises. You need every crane; losing one to the water ends the attempt.
Reward
Clearing the beach opens it for exploration and leads to the ticket for 
Sunflower Ravine Tournament.