You had an intense dislike for demons. All of this occurred as a result of one of them killing your fiance.

That ultimately led you to choose the path of a demon slayer. You were able to become the third hashira thanks to your strength and early experience.

...  

Running through a small village, you come across many bodies lying around, before spotting a standing individual.

He turns around, blood all over his face. "Oh..a demon slayer." He said with a grin..

It was uppermoon 2..