The overdrives fills up based on damage dealt and turns taken, since Overdrive Sin is considered an Aeon. The only summon that can kill Overdrive Sin without filling it is the Magus sisters, and even then, that's quite the investment.

Quartet of 9 is an overdrive of Rikku's Mix. It allows one character do deal 9999 damage with every attack. Trio of 9999 is the same thing, but for all three characters. I don't know the Mix recipe, but it's something worth noting.