Mahou weapons - no.
I missed this one before:
It's not very military, bit it is a space uniform. For something like this, you'd want to find something more like a fighting unit.
She's a weapon, but this is not communicated in the signature. You can't rely on knowledge of a character to fit the theme.
A city bombing I assume? I think maybe the flashes are a bit too quick, maybe add some smoke in the background?
About the theme:
I think maybe it would be easier for some to think of things like "wartime", "combat", "battle", "marching", "giant weapons", etc. Peaceful images aren't bad, but they are more difficult to find images for. Perhaps things like "remembrance", "honor", "duty", "victory", "defeat", and other such words might help too.
Remember that themes aren't always directly tied to the image you use, but also in how you present that image. The sum of the parts, if you will.