I don't remember the specifics but it was a manga about a guy going out on a date with his boyfriend but in the end it turns out that it was just the boyfriends ghost and the boyfriend was trying to stop him from ending it all.
May be in this first story ? -
https://www.mangago.zone/read-manga/ki_ga_au_to_iu_koto_wa/
So basically the mc (female) is experimented on and is turned into a literal sword where she is super powerful but is used to fight wars for many centuries. Somehow she is reincarnated to the time before she was transformed into a sword.
Sounds like:
The taming of the tyrant
https://www.mangago.zone/read-manga/i_tamed_a_tyrant_and_ran_away/
I Tamed a Tyrant and Ran Away