This is just a thought, About writing hopefully it turns out better then it sounds.
So here we have Sango and Inuyasha, trying to hurt down a demon that destroyed there lives.
After Naraku's defeat, Sango married Miroku and had 3 children, Kagome married Inuyasha,
1 son only.
but there happiness was cut short once more, This demon walked around with another demon with bright yellow eyes. The yellow eyed demon, That kill Sam and Dean's mother and father later on.
But this demon came with Red eyes, It wasn't a normal demon, It had it's demons, take over Kagome and Miroku both.
Everything was lost that night, Sango couldn't do anything but in that process, Her husband her kids all dead.
Same thing for Inuyasha too, They all were gone.
Kagome, Miroku, Shippbo and Kohaku and the kids were dead.
Kirara returned finding this, It was terrible, So Sango and Inuyasha, learn everything old school by killing everything possible, Sango change into a super Demon slayer, She trusted only Kirara and Inuyasha, That's all they had left.
Sango eventually found a aging spell, and others as well, She stayed young for 5 hundred years, Inuyasha took it too even though he wouldn't really need it, But they weren't taking chances, They were practically the best hunters.
Once in awhile they both would, Sleep around to burn off the stress. Sometimes loneliness, With other people not each other, They were like brother and Sister and kept it that way.
As for Sam and Dean there about to meet up with them, So let's get started. Please enjoy.