Who is Nero in Black Clover ? (Warning Spoilers for chapter 202)

So as we know about the devil in black clover has has power to devour mana and life from its opponent magical attacks have no affects so yami and charlotte seem to be useless aganist him.
But as we known the only guy with no magical power Asta is the only one who can fight the devil

The Devil

In such circumstances the nero tells finral to transport him back to the first wizard king statue where the nero breaks the seal on the first wizard king using the magic stones so as far as we have seen in black clover that first wizard king defeats the demon king is incomplete the actual story is that he  was on the brink of death while fighting with him and so to protect him may the nero sealed him away in the stone

First Wizard King

After awakening the wizard king says that he has has revived incompletely and this also leads nero to get to its real form which is girl with horns like a devil so now the question comes that who is this girl and why was the wizard king sealed by her did they know about time may for them to again fight demon like devil in present but this does tell why was she always after magic stones and also whats her reason to go only after asta is just because she is anti-bird or it has more secrets which is related to demon in grimoire of Asta.

Nero's True Form Scere

And As the first wizard king gets revived he sense the magic of devil from shadow palace as shown in manga.so now the first wizard may even enter in the battlefield to fight the devil.

Black Clover Manga Chapter 202