You should look into the "Showing, not telling" method of writing. You're not using imagery to your advantage, you're just telling the audience everything. "Riza is at the firing range." You could instead try something like "The piercing shots of a standard issue Amestrian military handgun rang out and echoed through the enclosed space as Riza fired round after round, each bullet hitting dead center of the human silhouetted target, true to her reputation." Set the scene a little.

The story pretty much ended after the first chapter because the whole plot, as described in your summary, was Edward trying to find the Miko Alchemist. "I have to find the Miko Alchemist. Oh, there she is." You are lacking massively in the build-up leading to the main goal of the story. You could've had a briefing of Ed being sent on the assignment and further in the story, he could've encountered enemies that are also trying to get their hands on the Miko Alchemist for crude purposes stop and fight him. Not sure I'll be reading the rest of this because your writing doesn't leave me wanting to find out more.

Your OC seems very much like a Mary-Sue. However, you have managed to craft a compelling beginning to what looks like it might be an interesting story.

This is an awesome fanfic