What Zeero said, except that you can block while the fireball is still out and it will still be active.
However, if you get actually hit, the fireball will disappear.
You have to be aware that they will be able to block after too many 5A/2A's. However, nirvana will be to attack again while they are in block stun.
The 3d isn't all that fast but the addition of a 5b, 2b, or 6b allows you to get the 6c out before they can jump. Seems to leave you in frame advantage while you do this anyhow, but beware of ragna, jin, litchi, and tsubaki's uppercuts. They can get you if they IB or trade with you.
To be on the safe side, if the 6C is blocked, rapid into more 5a/2a or 5b's.
side note, this loop can seriously mess up hazama if done right. He doesn't really have ways out until he gets 50% bar.