Humanity

Aru makes a f*cking sexy demon. <<<333

You obviously put hours of work into this, and I can tell that just from the picture, not the hours on the phone you spent with me telling me how your picture was going. This is some of your best work, and just by looking at it, I can tell you've greatly improved in your skill. The lineart you did here is probably the most elaborate I've seen from you. Aru's slightly messy hair, the long folds and rips in his clothes, the rips at the edges of his wings, the rust on his sword- these are all tiny details that really help the lineart.
Everything in the picture contributes to the mood you're trying to create, from Aru's hellish demon form, to the mysterious, foggy skies, to the barren landscape. I really like Aru's head and face, as well as the back of his wings. I keep staring at them because they're done so well. The elaborate shadows really add to his mystery and make him seem almost more dangerous, more unknown.
However, there are also a few things to be improved upon, as well. As Bored-dood said, the wings do seem a little out of place with a three valued shading, but this can easily be fixed by adding a few more values to the outer wings, shading the darks darker and the lights lighter. I also feel like it might be a good idea to add some texture to the (mostly outer) wings, just in a few spots, so we can tell his wings are made out of something different than normal clothing- they're wings, so membrane would probably be best. Maybe make them lighter in a few spots, or darker towards the top of the wing, the bone, where they would be strongest, and lighter towards the bottom.
Next is the rust on Aru's sword. Most of it looks pretty good to me, the only spot I think could be edited a bit more being the one in the very middle. The outside of the spot is a little too dark and the inside is a little too yellow for it to look like rust. Maybe make the center a darker orange color.
I really like the skull Aru's foot is standing on, it does add to the picture. However, it seems like it's a bit too large to be a human skull, especially if Aru is a larger demon. If compared with the size of Aru's head, it would be the skull of some even larger demon, an ogre or something.
Now for the last stop on my critique fest, the anatomy. Most of it here is pretty good. There are only a few spots I think could be improved. The mostly noticeable ones to me are on his legs. Here, Aru's waist looks rather small, and his legs look a little too slim. The legs should be slightly thicker at the thigh, which also makes it a little odd because the leg closest to us (not on the skull) is not seen through the holes in his clothing like the other one is, which means the leg itself would have to be very very thin. The other spot I see is on the leg standing on the skull. When Aru's upper leg comes out of his pants, there is a small line. This one tiny line makes it hard to tell how the leg is positioned. The way the leg is sitting, it makes it seem like it's facing to the side. However, this small line makes it seem like there is supposed to be depth, in which case the leg would have to be smaller towards Aru, and the foot would have to be darker on the bottom, the toes turned more away from the viewer. And this is just a small thing but I think the lines that create the depth of Aru's ears could be straighter- the top ear has the straightest and thinnest, and then the other ears while the other two have slightly wavier lines.
In the end, though, all of this is up to you to determine whether or not you think it was useful. I still think this is a great picture, and what is most important is that you've improved in your lineart and coloring skills, and that you had fun doing it. This is still a great picture, and coupled with that small quote from Aru, it takes on an even deeper meaning, because even demons were once human. And when we look into Aru's eyes, we see feral intelligence, but more than that, we can see his sorrow, and the humanity he still retains.