I think some of the main things you need to work on are color choices and the outlines
for example the hair has really light outlines compared to the other parts of her body
and because of it her glasses sort of pop out which I think was unintentional
as for the color choices the girl looks really washed out and drab
my guess is you took Mirai's color scheme and lowered the saturation to match the dark background.
what I think you should have done was edited the colors to have a more blue'r hue
or something to blend better with the background
I conjured this up on photoshop to give a better example of what I mean
https://i.imgur.com/AnKpYjW.png
(btw feel free to let me know if you want the imgur image taken down)
I hope this helps