You avoid getting hit with hard knockdowns, that's how. Honestly considering you control 3 fighters who pull from the same meter you kind of have be able to build meter quickly
Charging ki isn't viable. The startup/recovery is too long. On oki, every competent player is going to lock you down with an assist or the anchor's projectile. The only reason ki charge is there is for aesthetics. You already gain plenty of meter from moving forward, hitting, and blocking.