to.. impress your friends? ^^; well you see, that can't be your best inspiration for this... are you an artist/writer/musician of any kind? Are you familiar with inspiration? "An agency, such as a person or work of art, that moves the intellect or emotions or prompts action or invention." (dictionary.com) Do you feel a powerful urge to create this manga right away? Are you willing to work very hard, because you feel that it's worth it, even if no one else thinks so? Do you have a few ideas for it that you just love, and that you can't wait to get on paper? This is what inspiration does. I think you have to find a few more things to inspire you. ^^; sorry. (maybe read some books about fudal times, & if you find some weird or interesting facts, you can base your story on them.. that would be my suggestion, rather then read other manga from that time, because that would be like basing your story on something that's already based on reality. That's like... taking a photo of a photo or something. ^^; )
And also, lots of people have similar ideas, but no two people will do the same thing with an idea. ^___~. If you put enough of yourself into the story, people won't be able to accuse you of coppying <3
good luck