To unlock lime u have to have 50 Deadly Poisonous Jelly.
Then go to 4-8 and look for a secret path. When ur there, u should be able to see a lime thats on the floor at top right corner. After u kill all the monster, the Poisonous Jelly will disappear and lime will disappear after a few sec. Now you've unlocked Lime.
(Deadly Posionous Jelly Jelly is found in Episode 4)
*Only KLunia and Jlunia have Lime*