EXPLANATION:

Sid is evil. Aron is very smart also he is the doctor that can heal Cain. Sid send one of his lackeys to kill Aron but killed his clone so now Cain still doesn't know Sid is against him and that the actual Aron is alive and can heal him using some of the doors soul and sid knows Aaron knows that sid knows that Aaron knows and you get it...

Side note: Donut is fine. The door has no idea what is going on but he felt that he could thrust the doctor and the red-haired guy is very powerful but he is acting cute and all on the corner.

Call me sensei because I'm about to teach you a thing or two:

Sid tricked Cain into giving him the magic compass that looks like a star in an earlier chapter in order to locate a doctor to fix the wound on Cain's chest but Sid is an enemy and he located the doctor (the guy with the scars who is called Aron and is the only demon doctor that can heal Cain) and killed Aron's clone so that he can't heal Cain but now Aron is in front of Cain and he is trying to explain that he is alive and he really is the doctor because if Sid pulls out the head of his cone Cain will thing the real doctor is dead and Aron is trying to trick him because Aron used to be on Satan'sside but he fell in love with a human that was his door (and I thing died) so now he is not allowed back so he wants to side with Cain.
I think...