Decision?
Lex was stunned because that was the last thing he ever thought he would hear. He was powerful, yes. He had an ability which could make him nigh invincible, yes.
But surpassing an SS-RANK ability user was no joke. He didn't even doubt for a bit that he would last against Bella; if worse came, he would have to use his second ability against her.
Because there was no chance in hell he was getting even a single attack on her. That was his current situation.
For him to reach or surpass her, he would need an ability very powerful. Maybe Pyromancy. But he doubted Bella asked him because of that.
She could find other Pyromancers.
There was also the fact that Bella's ability was probably related to ice. That much Lex could understand from the observation he had done till now.
So, why?
Bella smiled, seeing the confusion on Lex's face. "Tell me something, Lex, why do you think only humans survived from the Dark Era?"