The Sheep Rustlers
Talk to Koyin to start the quest. Follow the objective marker located southeast of Hateno Village. The marker leads to Hateno Beach, right near the Hateno Bay. Defeat all seven of the monsters found at this location, which includes Black Bokoblin, Blue Bokoblin, and a Black Moblin.
Return to Koyin and speak to her for a reward of 10 bottles of Fresh Milk, completing the quest.
You told Koyin that you cleared out the monsters living on Hateno Beach. In return, she gave you a handsome reward.
You feel like you're getting along quite well with Koyin now! Maybe?