Any stories where the past-life memory doesn't instantly merge with the Protagonist's memories with the Past-life and Protagonist being two different people with the latter fearing that past-life will take over his mind?
Unruly Phoenix Xiaoyao didn't read the whole message, not exactly what u are asking but good nonetheless
Well there's (Ozpin/Oscar) from RWBY a cartoon or one of the protagonist in Wheel of time a western fantasy.
The one that comes to my mind is Haunted Duke’s Daughter, where a character is haunted by a reincarnation instead of fusing with them. Then there was Headless Villainess where the body seems to be inhabited by someone else, but unfortunately the translation was taken down because the translator didn't got a blessing from the author... after it was finished.