Hey everyone biggrin I've been gone from here for too long and I hope to restart up on my idea-dumping on something like this. If I get any new inspirations I'll update this post so that everyone can see them. If they get claimed then I'll edit it to have them striked over like so so as to not confuse multiple people. So without delay, here are some ideas I have:

gaia_angelleft Inuyasha-based: gaia_nitemareright
Within the Feudal Era of Japan, years before Kagome's arrival, a young priest initiated into a temple that housed a seal for a Greater Demon, ends up releasing said demon from her prison. Instead of behaving like most would (killing him out of spite for imprisonment) due to her higher level of intelligence, she insteads thanks the boy for her freedom and leaves him with a 'parting gift' for when they would one day meet again.
Said reunion would occur shortly after the shattering of the Shikon no Tama, where a shard ended up being lodged into the priest's body and began attracting various demons. This unintentional beacon for the various demons results in their reunion.... Story begins before the Demoness' release. Upon agreement, there can be run-ins with various cannon characters and/or involvement with cannon plot at their discretion.

.....and that's all I got right now. I'll update this on whether or not I get more ideas and modify on the status on each one as I go. Feel free to PM me or make a quote so that I may get back to you as soon as I can.

Sincerely, with full regards,
Nine-Tails927