Ah the colors are so mixed and dark >...<

For a bright vector, like Eeva-chan's the background usually
should be either bright or the vector should be darkened.

Athrun's side needs more work on it, the simple brushes
give it a low quality look. It's too simple and it just makes it look
very messy and as if it was slapped on.

Kira's side is also messy but not as bad as Athruns,
the clouds are too noisy and should have been blurred.
They were simply done and I can't see much of how
to criti rather than just say it needs more going on.

As for that blue/black could thing in between both
only adds to the randomness of the wall. It should be taken out
and perhaps putting Kira and Athrun closer will give you
less worry and let you focus on making both of their sides better.

Hope that advice helps :3