https://www.youtube.com/watch?v=gKyY05l_XQU

Small edits in the future are possible.
Changes made:
Full nether form no longer has red eyes, and the skin tone got a bit brighter.
Half nether form has the same skin and hair color as full nether form instead of having a weird "transition" kind of color.

Took me a while but here's what I got:

So yeah, Rogue is part Nether. Story-wise he started slowly turning into a Nether when he and his parents were attacked by one that could infect others and change them into one themselves. It doesn't affect his mind in any way thanks to a special magic called "love." Very cliche stuff. Regardless, he isn't too happy to become one and is determined to rid of all the Nether with Knight.

Midway through the story, the middle face above gets revealed after having an argument with Mage. Towards the end, horns start to appear, thus he can no longer hide his face with bandages. So no one has ever actually seen what he looks like normally, but I drew it out here anyway.

Finally, I tried to make his Nether form look "windy," as Rogue's affinity is the wind element. Windy things are normally portrayed with the color green, but I wanted to go for something a bit more blue for Rogue since that's his character color, which is what the ones on the bottom are. Oh well...

So yeah, I'm going with the greener one.
Also, what does it look like or remind you of? I feel like I've seen it somewhere before, but I don't where it's from... uugh, it looks so damn familiar though, it's gonna drive me nuts. I don't wanna be ripping off something and have no idea I'm doing so. If someone could tell me where they've seen this green skinned, white haired monster thing, I'd appreciate it. I wanna say it's from some old 90's/80's cartoon or movie... might be from a game though. Buh~...