I think the author was not writing a story where there’s an intelligent and planned out killer but writing the reality of it. I believe what Kamiki said about saying the address and at the end, the one who really ended up killing both Ai and Gorou is that crazy mf who lost in the end with his delusions. Kamiki used him and that delusional have a choice, to kill or not but he chose to kill because he believes Ai belongs to him.
About Kamiki killing other women, I believe that started after Ai was killed. He has the mindset where he’s already at the bottom or beyond saving back then so when Ai died, he found this no remorse of doing the same to other women. I’m not psychologist but I believe there’s a study like this, about the minds of a criminal where at the lowest point of their life who lost everything and no longer have any hope would resort to that action that made them feel a bit better. So it’s very realistic no matter what anyone says.
Do I forgive Kamiki. No. Never. I do feel sorry when he was a child. He never deserves a life like that where he get constantly SA’ed and raped and honestly, I blame that woman who planted that sick and twisted mind of his who started it all. If she was alive, I wish I can torment her, she deserves to get backlash by the public and not Akane.
Kamiki doesn’t deserve to get sympathy in his adult life actions. Only you have to when he was young but other than that, no. Ai is never coming back and if she ever reincarnated, it doesn’t change the fact that he triggered Ai’s death and proceed to kill other women.