i saw you made an edit on the satsuriku no tenshi wiki about his past and i'm searching a lot to find the novel that talks about it, but i can't ;-; can you say to me where can i find more information about the novel or even read it?
Unfortunately, no if it's online. No one has uploaded a translation of the novel no matter how hard I tried to find it. You have to buy and read the novel yourself. I even got it from a Japanese fan in twitter who bought and read the novel. But I do know it's legit because Satsuriku no Tenshi's latest chapter tells about Zack's past. I can only provide you these images as proofs: