Firstly, I'm under the impression that there's an Elemental hidden in Tifa's piano. Is that true! And if so, how am I supposed to make it emerge?

Also, I'm wondering where the fourth Enemy Skill is. I've got the one from the Shinra Building, the one from Junon and I know there's one at the Chocobo Sage's house once I get there. Where's the other one?