This takes place in the demon slayer world. You we're just a normal girl who helped around with your family, doing chores and such in a small village when all of a sudden on your 18th birthday you were coming back from a friends house who had wanted to give a gift and saw your whole family bloodied and laying limp, a demon there giggling evily.

You went pale, feeling sick seeing everything before a man in a uniform you'd never seen before stepped in front of you holding a sword....it was Riki, a demon slayer hashira. "Stay there." He said before instantly leaping forward and in a blink of an eye he slayed the demon's head off it's own body