So i suddenly gain a little interest in demon slayer.
I only reads some fan fiction I didn't see anime or manga.
I am more of a reader then a watcher.
So i don't know much about the real plot ok i am just telling you in advance.
Also I have seen that in fanfiction of demon slayer whenever someone get reincarnated or transport in the demon slayer world they mostly have sun breathing or they mostly have already created breathing I only find some newly created breathing. Also most of them are romance and yandera related. 

The breathing I am thinking creating about is nature breathing.
It's created by my own created Female lead she does not belong to any franchise.
Nature breathing first form to sixth form is all about giving demons peaceful death. There is no destructive power in nature breathing. Until I create

Because when my created female lead watch the anime or manga  in her previous world and see the back story of demon's she understand that some of them become demons because of some circumstances.

She also does not like watching someone in pain even demons.
So the breathing style she created is to give demons peaceful death.

Oh yeah also she will be not using sword or blade whatever
she will used a Scythe.
Because I think scythe symbolize nature better and when harvest you used scythe for harvesting.
It's like harvesting demons with a scythe.