Critique time
Well, first of all I guess I'll... comment on every character on their own, going from the right to the left~

Himmel
Meh, I personally think that you did a good job on him. The pictures Meltina drew of him were always quite detailled (like most of their work) and you managed it pretty well to draw him in your style. I also like his pose pretty much and yeah, all the crinkles are set on the right place. I just think that his right eye (from our point of view) has a... somehow a little bit weird form and somehow I think you could've shaded it better.

Amaterasu
I loved him on the preview most somehow and I personally think that he turned out best. His expression is... cool and with those googles and all... yeah. Actually I can't spot anything that irritates me in any way if I look at him lol

Selina
Hmm, Selina is quite... well on the one hand I must really say that I am impressed by her pose and this expression... THAT'S Selina *cough* And of course, good job on the crinkles and the coloring and all. The add of a book is a quite nice idea as well and it also got text on the pages now. But somehow the left part of her front hair (our point of view) buggs me somehow and also the light reflexions could've done better if you ask me. Like... making it a little bit more wavy and make it more fit on the hair *has problems to describe it* you know... this way it looks like all of her hair bangs would be like a flat layer because of those reflections. And I know that this is sometimes hard to do *cough* at least it's hard if you ask me.

Blade
Ketchup tin <3 You drew him perfectly and I can't spot any mistakes on him, neither in the design nor in the shading. I'm surprised that you managed it to make his body look like metal, I actually fail at those things. And his pose is interesting, hope he won't fall on his nose this way XD Just.... where did that 'o o? speechbubble' go? It seriously fit in there. You got to tell me how to draw poses like this o o

Soo, that about the characters and yes, I read the describtion, but still... somehow a background is still missing. Don't punch me in the face for this - it looks a bit weird with that gradient in the background. It was a nice idea, but I think it would may have looked better with out it. And... just for a tip in case of you want to do an easy background once again: What about something like a mirror ground? The only thing you have to do is to copy the characters and frip them vertical:

^{Edit » Transform » Flip vertical}

Then... just a little bit of scale and adding a gradient to transparent and it looks quite good. But that's just a little tip, you know? :3

Nonetheless it's quite visible that you put a lot of effort and work in this and it's not poor >: | I wouldn't be able to draw a picture with more than three characters in this time with such an amount of details and such varity of poses. As you said, the characters are all... quite different to each other and placing them on one picture together (in a way that is not completely senseless) is hard. You did a good job on this, so don't worry. I really like it, therefore... thanks a lot for spending so much effort in this picture I bet the others will like it as well :3

_{*cough* I want to know what's written in this book *cough* I mean... I'm sure that these are their plans for world domination, they are going to build something to pwn us all D:}