What are you confused about?
Basically, the story first happened in ancient time. MC was a son of a noble and was tasked with getting the demon core. That demon happened to be the snake demon who liked MC. The snake would get killed by god cus he's a demon, but the only way he can survive was to bury his core inside sth "sacred". MC betrayed the snake by not burying the core as instructed but gave it to the king to cure his illness. Tho, he MC was tricked because "sacred" could also mean the emperor's body, so now the snake accomplished his goal.
I'm assuming that he had killed MC 9 times (the first probably that first life) and kept the skeleton. The MC just reincarnated again and again, and got tricked by the snake again and again. The recent life was no difference, but I'm guessing since they mentioned "9 generations" and since he already died 9 times in the past, this life would be different.
Somebody explain this pls