Here's a description of the manga, it's completed. Read this like 7yrs ago?
Kid meets Woman who is like a cowboy? had like a gun?
She was a demon or something.
Somehow she turned into a teenager looking for the boy because he died in the river of styx but was reborn somehow (but the boy lost his memory)
Or something of that sort, some reason the title onihime reminds me of that manga, maybe it's the girl's name? i think her name is hime, not onihime.
Sorry for bad description
This post was edited by Uguu on Oct 23 2014 07:30pm