borax, Feathing: There's the
The Beta Place where you can have someone look over your grammar mistakes and help you with it. Not only that, the betas can help you wtih other areas like plot and characters. Check it out. :)
And borax, I'm not going to criticize your grammar since everyone already pointed out you need help with it. Yes, the reality is there are people who will judge the writer based on their posts before the story is even posted as for the most part the writer's posts and the story itself will be of same writing style. However, don't worry. Like I said before, there are also people who are willing to help you get better and also everyone starts out somewhere. This is a good place to start posting your fan fiction and get feedback. I also can't stess enough going to The Beta Place.
As for your story idea, sounds interesting. The way you explain what you aim for your story to be about reminds me a lot of a few animes I watched. I would like a bit more explanation on the plot and what's really going to happen, though. Like for instance, what's the situation. Is Team X trying to take over the world or trying to capture the legendary? Bad example, I know, but this is to give you an idea of what I mean by situation.