For your first shoot I think these are really good. I don't know this series but the characters' poses and emotions come out well. I really wanted to go to the Cosplay Expo but wasn't able to make it. The Japanese Garden location is really nice!
The main issues I see are some technical things.
I think some of the photos could be cropped to avoid distracting things, like this one:
Be careful with on-camera flash. Sometimes it helps when you use it as fill-flash but when the flash is on-camera the lighting always looks flat, without shadows to show the shape of your subject. It normally looks more natural to use off-camera flash or bounced flash.
Be very careful, especially in direct sunlight, to avoid clipped highlights. Most of the photos with direct sun have some clipped highlights, which turn a funny green color before turning white. Clipped highlights in the background can look ok but clipped highlights on skin or hair looks sort of like a digital disease. When you review the photos watch out for blinking areas that are clipped (you may have to turn this setting on). I've never used this camera but it looks like there are some other settings with exposure and dealing with highlights like HTP and ALO that are worth checking out:
If you shoot RAW you may be able to recover clipped highlights when post processing on your computer too.