this is just an idea so far, i dont really know where to go from here. I was just playing around with some new brushes i made and first i just had misa, then i added raito and L. I'm gonna have text somewhere, but there's too much plain black that doesnt work with the intricate grunge so i need som suggestions on what else or anything i need to fix.

please please full view you cant possibly see it from the thumbnail.

An interesting idea with the grunge patches but right now each piece looks rather disconnected...perhaps if you tried a stylistic element that would connect some together in a logic pattern? ...extending the grunge patches in order to subtly connect pieces or using a lighter (brown?) background rather than black with a texture?
You could keep the fadeaway look of the focused pieces while having the background blend more with the character pieces

Another item in addition to what was said by cyd84, is that you need to create a focus for the wall be it the characters or somethin else. It currently isn't focused on any thing identifiable. As far as the text is concerned remember to make sure the text either runs across a continuous color or stands out enought to run across color gradients.

Same thing with the focus and...just a random thought, but I keep seeing gun crosshairs in the back of my mind when I look at this. Just a random thought.

Like what was said before this post, consider making a full grunge background and lowering the opacity more at some parts so that it looks like its there and yet not.

As for focus, maybe a text would help if you don't want to add a large-sized character.