Regarding MomokoKills photos, On Sheijy, I like the Spiderman-like pose, the diverging lines of the railing and the low camera angle. The waterfall and grey textured walls make for a nice background. The highlights are a bit blown out, bright. The composition might be a bit stronger if there was less floor and more background showing above the cosplayer.
With Zelda, I do like the expression on her face. The sun peaking through the plants looks nice. The flowers make a color background, but I would have liked it more if the man-made things were cropped out, such as the concrete wall and white supports to the top left of the frame. Her arms being cropped out also takes away from the image by leading my eyes off the photo. If her hands were included in the photo, you could show off more of her costume.
The Boba Fett Portrait has a nice, clean look. because the background is so simple and not distracting. I do like how his head contrasts well against the brighter sky. I would suggest using the rule of 3rds to place the tops of the trees at a certain height.
Both Fisher portraits look good to me. I like how you placed foilage in front of the cosplayer, putting him deep into the environment and creating more depth in your compositions. The brightness of the backgrounds could merely be an artistic choice.