I don't know if I recalled it wrong or not, but I wonder who was PL Yoon killed? PL Yoon approached Samael and said "I killed that child for you," so who is this child then? Or is it Shedim, and not PL Yoon? Because the figure is in all black, but look at the hairstyle i thought it was clearly PL Yoon.
Also it makes sense since Present Yoon afraid of blood
I think that scene should be Shedim? because that aligns with him confessing he killed Yoon to Samael from what I remember. All the characters have the same faces as before but Shedim and Yoon's hairstyles look super similar and then there was a gray filter for the flashback . But I also may not remember exactly - looking at the raws I realized that the dialogue is very critical to follow along.
If it's Shedim, then the child he mentioned was PL Yoon. Maybe this is also why Samael hates to be "stuck" with Shedim (I don't know if this is true or not, I recall the Tiger Spirit mentioned it before). Regardless, I really want to see their past life to know exactly what happened. I agree, the lore building is quite interesting (=・ω・=)
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.