The new Keyblade apprentice.(Kingdom Hearts Birth by sleep)

Not everybody knows that there are other Worlds besides their own since they're all kept secret for lots of special reasons. There's a World that it has 1 Master who trains his other 3 Students very well, but what happens when somebody new has arrived, and something wrong with her heart??? Could there be someone interfering with her heart ever since she's arrived, or if somebody's hidden deep within her heart wanting to hurt her life??? As she met many different friends, and has a boyfriend, will her life ever be saved from the darkness???(I only own the new Keyblade Wielder named: (Cosmic), and the ideas, not Kingdom Hearts birth by sleep)