Hi Alexander. I am a professional photographer. I like the lighting on your subject in each shot. It's soft, which makes the shadows less distracting, and more natural.
Your locations don't seem to fit the characters, except when you blurred them, and kept them simple. I know, the venues for Cosplay events can be limiting on appropriating scenery, but try your best to find them, or find a relatively simple background that is interesting enough, without be distracting.
I like that you had at least one pose looking away from the camera. Do more of those. It will make them look less posed, and more natural.
The second photo is a nice pose, and shows the costume well, but again, the location seems too modern for the costume.
Be careful not to over-expose the brighter parts of your photos.
If you want to get even more natural poses, you might try having them move during the photo. You can get hair and costume to flow in movement.
You can see my huge gallery here at Cosplay.com at this link: http://www.cosplay.com/member/150562/photos/
Here are some samples of my action shots: