I feel there's a ton of untapped potential in this setting.
For example, Misaki-chan: she looks like a warzone refugee. She isn't even wearing an uniform! That's not the normal look for a high school romcom heroine. Both readers and people in-manga should be complaining and demanding that she takes a bath, combs her hair, wears a proper uniform, etc. etc.
And the blonde beribboned loli, will she be ok? Yeah, cuz if you look closely, she's a loli... haha, I guess it was the obvious addition to this cast of romcom heroines: if you've got osananajimi, tsundere and kyonyuu, the obvious fourth is a loli. I worry about her safety in a war manga, what's gonna happen to her??? (Actually, my little bro said that the answer is evident: "She gonna die in 10 minutes, DUH!" But I hope that's not it...)
And Misaki should have an impressive set of survival skills, seeing as she has been living and scavenging in a war area for some time... she prolly can use guns, jury-rig all sort of devices, fight with improvised weapons, make a campfire and cook food on it... but, so far, she hasn't had the chance to put any of these to use... that's a side of her that should definitely be explored...
In conclusion, leaving this manga as a oneshot is a crime. I demand a series! ヽ(͡◕ ͜ʖ ͡◕)ノ