Here is the full list of all 15 Rakuen achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Return all of Sue's marbles.
Learn 'Mori no Kokoro' Part 3.
Learn 'Mori no Kokoro' Part 2.
Learn 'Mori no Kokoro' Part 1.
Become Radical in the eyes of the Radshroom Protection Society.
Help save Bad Attitude Onion from his bad attitude.
Collect and place all the special items for the hospital.
Complete the game.
Learn 'Mori no Kokoro' Part 4.
Learn 'Mori no Kokoro' Part 5.
Help the Wooden Sign on Wooden Sign Day.
Collect all the jukebox tracks.
Adopt all the pets.
Discover the Leeble Protection Agency.
Examine each unique piece of Monsieur Bud themed artwork.