It only works if you have keys, you can't use it to get multiple non-key drops.
1 key= 1 drop
2 keys= 2 drops
3 keys= 3 drops
ect.
You can farm keys by having a level 15- invite you to their party and running low level abyss dungens with them. The bunny at the end will almost always give you a key. You can just deposit it in your storage so its not used up on your next run.