Rule of Rose

Costumes:
After finishing the game with the Good Ending, you will get a Four Leaf Clover Key. Once you start a new game, the key will be in your bin and you can now access the four leaf clover room for extra costumes!

Nurse: 
Get Good Ending

Tennis Instructor: 
Get Good Ending

Gothic Lolita with Maid Brown: 
Get Good Ending

Brown as a chair: 
Inspect Chair in 4 Leaf Clover Room

Octopus with Crab Brown: 
Find "October Ticket" in 'Once Upon a Time' Chapter

Rag Doll with Stuffed Brown: 
Find 4 "Broken Robots" in 'Rag Princess Sews' Chapter