Windstar
[12] Conqueror
If I didn't like playing Lightning and Tifa so much, I'd main Kain. The main issue is that he's too reliant on his assists to really beat down his enemies, and even then it has to be one of the God-Assists (Kuja, Jecht, Seph, Aerith) to maximize damage. OTOH, his assist building is stupidly good. Between Cyclone and his dash follow-ups, Kain has no issue building meter, and Jump is just godly, especially during those rare moments where you land it on reaction.
Mmm, I dunno. Kain's only really problem is combos which is where the assists come in. He can get guaranteed HP damage off any of his wall rushes. Its just landing his more powerful HP moves (Gungnir, Rising Drive, etc) require an assist.
Tifa feels like she has bigger problems to me. Too much of her stuff ends up in Chase and that's always a 50/50 on whether you're going to land a follow up or not. Her feints aren't that great, either. Still I do enjoy playing her.
By the way... Gilgamesh and Paladin Cecil are also pretty good assists.