Interesting idea it's a little different from what most mangas are doing in creativity of location and time. Go for it. If you post it up here I will read it. But be warned don't expect too many people to reply to your work. I have a fan fic here too and after the first part people just read it and give no response. Some people don't like it to have their work critized and some do. I'm one of the ones that does like it. Anyway if you want some ideas read some of the other fanfics here. My fanfic is Magical Detective Daisuke. Part 3 is just came out so feel free to read it. Solid came up with this weird crossover .hack/Daioh so read his manga too. Good luck with the manga idea.