I’m Not a RegressorNot a Regressor

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Firstly that shin hyak (returnee) guy is a dumb f*#c we will see that from the first chapter like absorbing a different stigma, that too Lyra's. and what kind of moron forgets the person he left to die when he is so kind and righteous.
we see that mc doesn't have the full black sky and there is another actually heavenly demon that also has a black sky and he is hiding and needs to kill the heaven-defying star(returnee) and absorb his power to complete his black sky

Ok theory time I think that lee shin hyak guy is the actual heavenly demon and sealed his memories like a split personality thing or another body thing and is hiding among the masses and propped up MC as a heavenly demon in his previous life because as we can see
in the previous timeline
1)he is abnormally stupid for an awakened
2)he also forgot that he killed mc (Left to die)
3)also subconsciously tries to build a relationship with haeun when she comes to the gate to find MC (who is left to die) she is hot but she is also a rare 7-star awakened of the dragon constellation with that weird dragon eyes (cursed at the beginning of the novel) that help in controlling dragon heart
and doesn't connect the dots that it's the same guy (my because of MC's lies, he is dumb after all)

current timeline
4)We know that memories get raised when we use active black sky powers, that is how shin hyak must have survived the dungeon
5) After regression he is seen to have a creepy smile on his face despite his plan failing
6) Also when he enters the demon kingdom he hears a male voice noticing his arrival
I think in previous timeline, at the end when he defeated the Ojin heavenly demon absorbed his power (because black sky is a cheat it can hide your absorption) he was still, not powerful enough to absorb vega so he wanted to go back in time with all this knowledge and die erasing shin hyak the sub-body and returning to the main body with all the knowledge with cutting off his trail there. He has all the knowledge while MC only receives snippets in shin hyak's pov, he is fattening MC like a sheep through those memories. Otherwise, the actual Heavenly demon would have noticed MC as the heaven-defying star due to his growth rate and would have taken action.

I know this theory has a lot of holes but the author seems to be righting many coincidences twists like Isabella being leech queen and her sister serpent queen.