beta
To everyone lost, it should be coming up in future chapters an explanation soon. Despite the smut the lore building is actually really interesting.
From what I could tell from the raws (may misremember some details), there should be a flashback where Yoon and Samael met in a past life. Samael may have been an angel or something on good rather than as a demon now, he was wearing a priest uniform. Shedim was also there and seemed to look up to him. Suddenly they met Yoon (previous life) who was injured, and Samael cared for him.
For some reason no one liked him associating with Yoon, but they also seemed to be getting romantically attracted to each other. I assume Shedim was feeling like he was "corrupting" Samael and so he then went and killed PL Yoon as a favor. He told Samael/Samael came back to that and Samael was so depressed and killed Shedim/others? I only recall the panels showing him with blood after that. It seems then he was/now currently in punishment.