It’s been referenced a few times that Ashvalt killed a handful of the Rogue Family mages back in during the fighting prior to them stepping back and letting the Consul rule (the accord). Stopping Ashvalt once was of the reasons they agreed to the accord (once Regin’s family and Camilla were unified with Ashvalt’s side, they were a difficult faction to fight); for Ashvalt, he saw it as a narrow victory condition after growing a bit older during the fighting. Ashvalt is probably the one the Rogue Families fear the second most after Camilla, though neither of them have the most powerful overall Family among the mages they are individually strong duelists.

While he is ruthless, as we’ve seen his children tend to be somewhat more… sheltered from the violence compared to a typical Family mage. Ashvalt viewed the accord as a way to end the violence and not have his kids inherent the fight. He was pretty actively looking to resume the fight during the Family meeting, but if we recall that was after he believed their plots had almost gotten Arkady killed. Now that they’ve made a second attempt on his kids, he seems to have lost what little restraint he might have had from the accord, deciding that there is a second path to building a peaceful world (killing them all).

Of course, as he is an important figure in the Bureau now, the summary execution of someone without due process is probably going to have some ramifications.

Ashvalt isn’t the strongest of the Family Mages, though he’s a dangerous one. This magic is not actually his innate magic talent, and his innate magic talents aren’t that great, but he’s put a great deal of effort into honing his ability to fight other mages, and tends to be brutal in how he fights. Normally Saraine would be a fairly bad match up for him, as he doesn’t have a good way to stop Void which activates faster that magic can normally be calculated, and Ashvalt doesn’t have any particularly good counters to that (Camilla has several, and unlike Ashvalt, has very powerful innate abilities, which are harder to stop), but when Ashvalt heard that Saraine couldn’t use Void, it eliminated the main trump card Saraine would have in a fight. While she might have been able to win a prolonged fight, Ashvalt believed in raw speed he could beat her to the draw and punch through her default defenses. Sort of like how Naomi often beats mages to the draw just by punching them in the face – sometimes the magic you can use matters less than how fast you can use it. In this case he used a simple magic that’s generally used for defense offensively, and he simply made a barrier faster than Saraine could… he just then used as it chop someone in two instead of block. Saraine was probably trying to use the same magic herself (as she did to block Naomi), Ashvalt was just, as he predicted, faster.

It’s not particularly clear from the comic, but Ashvalt’s been able to hear what is going on for quite some time (for the same reason he was able to find them, his son activated a sort of emergency tracking bug when he was kidnapped).

Anyway, that was a long ramble, I just sort of felt I should give Ashvalt more background than he’s gotten so far as sometimes I worry we don’t see enough about the background of things.