Matsuo Hoshino will appear in the Select Plaza far into the game after rolling up the sun as per the Dog's request.
You can't start Matsuo Hoshino's level until you have rolled up all 39 cousins.:
Once you have rolled up all the cousins, you can play Matsuo Hoshino's level, which takes place in the flower meadow (Ikebana Teacher's level). Here you will find all the cousins and you have as much time as needed to roll them all up.
Dipp and Ace can cause problems, though, since they like to quickly run around a tree making it hard to get them.
THIS IS HOW TO DO IT. And if you play as Dipp or Ace, you will only have to deal with one of them instead of both.
The achievement will unlock after completing the level and returning to the Select Plaza.