If the First form of the Ashura multiplied Noah's attacks and allowed him to fight when outnumbered, the Second form condensed those ethereal sabers into his six arms, vastly increasing their power.
As for why Noah couldn't use it until that moment, it was because his body simply could not withstand that much power.
There were more than twenty ethereal sabers after all, a rank 3 body could not endure the pressure created when they were concentrated in six arms.
'It still hurts a bit but the liquid "Breath" in my body will keep me going.'
Noah was pushing his body to its limits in order to perform that technique and fight on the same level as the leader.
Also, the physical empowerment of the Demonic form allowed him to match the blows of a rank 4 beast, even if just those of a weak one.
'Even with my full power, I can only match it for a short amount of time. I can't resist that many clashes, my body won't last that much.'
