How Setsuna uses the Void.

He was already getting the hang of Void Fire. The first thing he learned was that, once Setsuna gave the silent order for the fire to chase him, it moved independently of its creator, so distracting or attacking Setsuna did not stop it.
A few deaths and resets later, he found out that the black fire could apparently see through solid rock, so hiding behind a pillar would not stop it.
On a side note, death, most of the time, was very uncomfortable. But he guessed that had everything to do with the fire and the lightning and the neck snaps and the spear-tipped tails and stuff.
After the next reset, Setsuna explained to him that Void Fire was naturally inclined to extinguish living things, and it could "feel him" somehow.
He eventually found out that the only way to get the black fire to stop chasing him was to get beyond the range of its "perception." He estimated this range to be somewhere between eighty to a hundred meters. Conveniently enough, Setsuna could not command the fire beyond the first instruction, so he could get back within range without fear.
Beyond dealing with the lingering flames, there was no real technique to dodging Setsuna's shots. Whether it was a barrage or a large fireball, it was simply a matter of speed, reflexes and finding the gaps in the offensive.