Idk if I'm mistaken, but is Dan killing people because he want to do good deeds? And maybe the reason he's doing it (yknow punishing sinners w his own hands) is because he want to be good (not that he's actually good) but yknow "good" in his own way because he did that in the past and want to repent. Idkkkk if I'm mixing this up w another manga since it's been a while since I last read this.
It was mentioned in the past chapters that he's killing bad people as a hobby and also to earn "good deeds" so that he can go to heaven and meet his "good friend". And people are now just realising that maybe that "good friend" was the guy that he was obsessed with in highschool, that he drove into committing suicide. (Correct me of I'm wrong)

READ THIS MANGA, ITS CONNECTED TO BRUTAL.
https://www.mangago.zone/read-manga/trace_kasouken_houi_kenkyuuin_no_tsuisou/
DAN APPEARED AND GOT MENTIONED IN THE FOLLOWING CHAPTERS:
15 20 21 29 31 32 33 36 37 38 39
I know that dan's already pretty fucking crazy but this manga just ruined his whole image for me. We don't really know yet if its fr and what's the reason behind it, and maybe I'm wrong cause it's still not done yet, but it's really not looking good for him... Apparently he asked his classmates/servant back in highschool to bully a guy he's weirdly obsessed with(the guy killed himself because of the bullying and dan literally layed down in that guy's grave while its raining, got hard while thinking of him(?) and drank a coffee with that guy's glove in it..) and dan also asked his servants to rape that guy's sister... And he's also pretty fucking ugly in that manga.... Or maybe he's just old? Idk idk... I'm still not that sure, I'm just making judgement from what I have seen so dont jump me..plz