I don't get the vice president, maybe she just likes him for some reason. Or doesn't get implications
I think something happened to her in her past that made her be supportive of his ideology
She has a scar on her face hidden by her hair. It’s been heavily implied that someone seriously abused her in the past and that Kai “saved” her from them. His feelings of guilt over to not preventing this abuse before it happened seems to be what’s driving his little child murder crusade. He’s trying to prevent what happened to the vice-prez from happening to anyone else. He’s still worse than all the people he targets, he’s a fucking serial killer, but he genuinely believes that he’s saving “Victims” from “Abusers”, even if his perceptions don’t actually match reality. Righteous violence is still violence, after all.
I actually find him really interesting as a villain. He’s like the personification of the general attitude in fandom spaces to uncritically exile anyone perceived as problematic, without any consideration of their situation or an allowance for them to improve, but taken to its logical extreme.
He’s so set into the victims and victimizers duality that he ignores the ways the people he classifies as victimizers are themselves victims. He can only see the world in black and white (and not just because this a manga) and he hurts people as a result.