finally, a manga/story that brought up the talk about this concept.
"reincarnation", "possession", or worse "taking over". those need to be put a line on it.
reincarnation mean both is the same person. the previous memories just sealed and awaken in certain times/ages.
possession is like the second souls is entering the body but goes as much as either can communicate with the body souls, switching turn or merging into one. or it can also possessing a lifeless body where it derailed from the plot and the original is dead so the "plot" need a soul to take over, or it a case where the body owner trying to escape and switching soul with someone else (i had read this plot once but i forgot the title. basically some kind of Princess/witch doing a ritual and switched the soul with someone from earth. it a manwha i think).
and there taking over. it basically (worst case) kicked out the original soul and taking it place. (i remember about certain manga with this plot, basically a soul entering a princess body and kicked the soul to take over her life. poor princess)
there also one more. that one is "inheritance" which is less cruel towards the original body owner (basically a soul passing it memories, power and Knowledge to the person. Thought it often sought confusion if it their memories or not since it harhard to know unless the owner of those memories or someone else told them directly).
also i need soiler of story from here on please