Unlike previous Katamari games, this game has a very simple achievement list.
You don't need to 100% the collection.
You don't need to collect the presents.
You don't need to roll up the Cowbear.
You do need to:
-complete all the levels which are "requests" given by "fans" that you interact with throughout the game's hub. Some fans have a single request while others have multiple, requiring that you play their level two or three times.
-collect all 39 cousins. Video here:
https://www.youtube.com/watch?v=DEERUVkuJAE-roll up the King and the Queen who appear in the final level given by the Elephant and Bird
-play the five super easy new levels as the king in a new area called the Royal Reverie
-roll up 2000 different items, which will come without any issue through progression
The King and Queen are HUGE and require reaching 3000+ meters in the Bird Elephant level, which can most easily be done in Eternal mode (unlocked after completing the level twice).