Nial disappeared soon after he got to know that he advanced to the second round. There was no need for him to stay in the Colosseum, especially since many Runiciers frowned deeply at him.
He felt like he was going to get killed by the envious Runiciers, who were unable to accept the fact that someone at the Lower region of the Mirae rank was a better Runicier than them.
Usually, the higher a mana core rank the stronger their control and perception of mana. That was why most Runiciers would also focus on the advancement of their mana core's rank, especially since the difference between each rank was ginormous.
Thus, it was even harder for them to accept the reality that Nial was simply a better Runicier than them!