For the vocaloid fanart: Overall I think it looks good. The soft color pallete is a good choice, and the clothing looks pretty good.
These are some things I feel like you could improve upon:
The bed is a bit too bright. Since it's brighter than most of the other colors, and it's a very large object, my eye is instantly drawn to it. It makes it a focus of the image, where I don't think you want it to be.
Also the way the sheets are drawn under miku (especially under her butt) they just kind of make her look like she's hovering over the bed slightly and not actually sitting on it.
The way miku's legs are bent looks a little unnatural. Her thigh and calf don't look like they're touching each other at all and they should be.
For the character design commission, I understand if the commissioner requested this, but the purple background blends in with the character a bit too much, since the main color on the character is also purple.