NERO had a secret.
While he was "sleeping," his consciousness and soul were sent to the dimension where his Soul Beast resides. He spent the past three years taming the wild beast. The time that he was able to win against the ice wolf in a fight, he finally accepted him as his master and allowed him to give him a name.
He chose the name 'Zev' because he read a story before where the wolf was named that way.
Anyway, he pretty much got along well with his Soul Beast after he tamed him. He became his sparring partner. In that dimension, his soul felt like his physical body. Aside from improving his physical strength, he was also able to learn how to control his Mana properly.
But of course, the only thing that he was able to train was his mind and soul. This was the first time that he applied the things that he learned on his physical body.