Dude he just appeared in like 5 chapters & there are even more family heads to appear in the story and you want SIU to tell their life goals to you? I don't know what type of story you're reading to come to that conclusion.
Wasn't it said before in the story that the slayers are there just for propaganda against Jahad empire. No regular can ever defeat an irregular. Hell Arlene & V couldn't defeat them let alone these chumps.