Tifa is an optimistic, happy-go-lucky girl. She's kind and generous, though she can be brutilly strong. She lived with Cloud in a small town called Nibleheim, and stuck in her mind they were good friends. The truth is...well, I don't think I should give it away...
I really think Tifa and Cloud make a wonderful couple...I wish they'd just get together happily ever after... But Tifa doesn't seem to get anywhere with Cloud speaking to him. Oh well.
Tifa's HP doesn't match with her level as much as other characters, and she also may not seem very strong. Her ultimate weapon, Premium Heart, is strange, and her strength seems to often change and vary from 7000 to 30 with it equipted. There's more about it in her weapon page.