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.
Complete the game.
Learn 'Mori no Kokoro' Part 5.
Collect and place all the special items for the hospital.
Collect all the jukebox tracks.
Adopt all the pets.
Learn 'Mori no Kokoro' Part 4.
Learn 'Mori no Kokoro' Part 3.
Discover the Leeble Protection Agency.
Help the Wooden Sign on Wooden Sign Day.
Examine each unique piece of Monsieur Bud themed artwork.
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.