A Japanese soldier discovers his world around him in shambles when he survived and people perished during World War II.

Internal and external conflict might be something to consider, the arrival of the allied forces and their behaviour on the mainland both good and bad clashed with a lot of the returning defeated infantry man, perhaps he has to learn to work with his recent enemy to achieve a certain tangible goal?

Wherever you choose to goal with those elements, I strongly suggest you ground the story in a lot of strong, well researched ideas.

Best

Jim in Japan.

IvyEight6,
With proper research, this logline could be based on a true story which will greatly help your marketability, but please mind the respect a premise as this deserves.

Great points from Mathias, I made him an Infantryman instead of a Major to ramp up valor.
“A surviving WWII Infantrymen must lead his fellow citizens beyond the nuclear blast zone of Nagasaki, Japan”

Take care.