It was a good story, although it creeped me out as well. The line at the end was also fitting to the manga. It surprised me a lot though.
No, it definately won't appear in the anime without killing the plot. I'm not complaining though - they already incorporated the other three gaidens into the anime, along with some of the omakes. That was nice enough. ^^'
The weird thing is that I got this empty feeling after reading it. Kinda like when all's said and done, the brothers won't recieve redemption either. Sorta like foreshadowing that in the end they'll just be happy to be alive, or at least in the manga. Just an odd thought.
Also, if I remember, one of the characters was wondering if it was really the girl's soul in that body. Made me wonder about a lot of things.