This minigame is actually pretty fun and easy.
You can do one hide and seek (HnS) game at the time, I mean only one HnS unlocked at a time. For instance, you have to complete level 14 before you can start level 15, no exceptions.
Sometimes this HnS locks until you've finished a part of the main story. An example: HnS locks at a certain level until you've learned chakra concentration. You will need level three Chakra Concentration for the later levels, so all those levels are locked if you haven't learned Chakra 3 yet.
You've got plenty of time to finish these minigames, some may take a try or three. He hides as tree, behind a sheet of fabric, or in a pot. Finish 20 of these for the achievement