I never really thought about it but his nervousness about killing might be the reason he does a long monologue before killing anyone. By building up his courage and justification behind what he's doing. 

Now everyone is curious about Rynn the Red.

This back story was certainly pulled out of no where just to give her a reason to agree. Before it was made to believe he was cruel to her since the day he made her a shadow with blood worm. 

Dunno why the demons are scattered and just sitting around waiting and not locked up or buried in a pit somewhere, but there are 7 other demons that could have possessed Jake. Wrath would be my pick, not the fake gluttony one following a former assassin. 

First off, it's already stated that the dominant personality is the current Samael, not his previous life. Even if it did influence him, he was a con artist and maybe a thief. I believe he mentioned being in jail? Either way, it doesn't add up to any kind of upstanding citizen. He may wish to do better but people usually fall back to what they're used to. Ultimately Samael is selfish and will continue to look out for number 1, himself. This is even more so because he knows the future and that becomes his justification. 

He is trying to survive in the world to avoid the spirit king bad ending but he is starting to look like an alternative bad ending himself. 

Don't tell me the girl that Michael failed to save was the nun's sister. That would really make me want to choke the MC.

Aw don't tell me she's an executive or something in the syndicate. 

Must feel nice to get his villain monologue moment. 

I'm not sure where maturity has anything to do with it.  The MC is an asshole playing his own game and actively disrupting everyone else to push his plans through.  Anyone would be pissed off working with someone like that regardless of maturity level.  And frankly speaking, anyone would reel in the line when they caught such a big fish.  It'll take a real pro to notice two fishes and be able to reel both in.