Hmm well you certainly didn't leave much room to make surprises, still I can come up with something.

Okay what if instead their attack gets publicized and a character ends up being seen out of their nightmare. This would then lead to heat from Britannia and could give rise to Japanese moral thus setting the ground work for a larger battle. 

Or you could have a character discover a geass and yes I know it seems a bit early and tacked on but still don't fix what's not broken. Although you could have an enemy have the ability thus forcing something to go terribly wrong. 

I can come up with more ideas but they would need to be after this mission because you have already fleshed thus out to a complete mission. If it was more vague or open to unexpected I could give better ideas.