Sergeant Kai takes responsibility for the hardest missions, earning himself the nickname "Iron Heart". Kai claims that he's doing it for promotion but is there something more behind his ambition.....?

The story is set in the year 2050, in a place called Sky City Tokyo. The main character, Park, is a window cleaner. If you've ever experienced those street windshield washers that descend upon your car when you stop at a red light, you can imagine what Park does for a living. Except worse, because in Sky City Tokyo, the cars travel in mid-air! How does a window cleaner become a hero?