I'd think that a game that'd bring characters from all over would have something that could break the universe. If you were to put together a party of three to nine characters who would you choose. They wouldn't exactally have to have to power to save the universe or anything, but they could. Just have fun with it.

Anyway the party I'd put together would include

Celsius (Tales of...)
Rydia (Final Fantasy IV)
Etna (Disgaea II)
Elly (Xenogears)
Samus (Metroid)
Ukyo (Ranma 1/2)
Karin (Shadow Hearts 2)
Aika (Skies of Arcadia)
Sailor Mercury (Sailor Moon)