They'd have to be instantly recognisable as a Final Fantasy character. Cloud is, of course, the obvious choice, though as Raistlin said, they seem to love Lightning right about now. Either would be a good choice; sword characters are popular in those games! However the OP stated it must be a Nintendo based character, which limits us quite a bit.

I would say Terra is probably up there as being a well known character, although a moogle or chocobo wouldn't be too hard to imagine in there. Kefka would do alright, too. Nice to see a villain getting the main spotlight. Cecil or Bartz might be worth a shot too, or perhaps you could have Rydia fulfil a role similar to Pokémon Trainer and use her summons.