I expected this chapter to be the results of a popularity poll but no one said his favourite character. Well, then, I have some facts about Beat's powers that show that if he had to kill Aurora or Dahlia had, they wouldn't need to fight.
First fact: Gravity Magic. Dahlia and Beat can change the time flow with their gravity magic. Unless Aurora had infinite mana she wouldn't be able to resist the timestop neither rewind the world to the point she wants. So if Beat and/or Dahlia had to fight again Aurora, they can just use gravity magic and all done. Gravity Dash of Dahlia for example is as fast as Aurora running in accelerated time.
Second Fact: Traits. Beat can predict when Aurora uses her time magic, so he can stop it attacking her. But also, he can predict what will happen inside the stopped time, so he could prepare a way to avoid that. Beat is more than capable to avoid that. In worse situation we have seen him. Dahlia's trait leaves her body avoid the damage, but nothing more. She cannot predict attacks, so in this case she would have to use Dark Ghost(which she has again now).
Third Fact: In target 47: target Dahlia's determination, Dahlia used a little of gravity magic to use her trait to avoid the Why? She changed the time of her arm, to make the timestop useless. Then the trait of Dahlia made the arm avoid all the hits. So yes, Dahlia is far more used to use Gravity magic than Beat so she knew about Fact 1. Why didn't she use it? Because it would take time. And if Beat learns it he'll do it too.
So time magic is useless against Dahlia, until Beat learns that fact too he'll be more or less vulnerable to time magic. Still, with Dahlia near, Beat shall learn it in no time.
The question that I sense that is important: Dahlia could defeat Vath(read militos2 if you don't know him)?
No. Dahlia is unable, for 3 reasons.
1- She can be quick, but the range of hit of Vath seems quite big.
2-Vath can use magic, so with Dark Ghost it'll be impossible to resist magic hits. As a MS, Dark Ghost has the power to be like a ghost. No physical hit can damage her. But magic yes. Of course as a monster she could do that, but her weakness is her power. She cannot hit others while being ghost. She must control when she goes ghost or not.
3-Vath has more power than Dahlia, since he absorbed power from players. So if Dahlia recieved a magic hit, she would die. Without the extra power, Dahlia would defeat Vath.
Well all is over now, I'll put the complete part. I really hope that it's good!