The G10N Fugaku was a intercontinental bomber designed by the Japanese corporation, Nakajima Aircraft Company, during WW2 for the Z-plane program. It was to have 6 engines, have a stepless glass cockpit similar to the B-29, and would’ve used the northern jet streams to increase range and save fuel (a similar concept to the Fu-Go balloon bombs). It was to be used like the infamous German Amerika Bombers, with the goal of being able to strike American industries. Due to numerous problems, such as rival bomber designs, an engine design too complicated, and the lack of resources needed for the Fugaku, the project was cancelled.
The F-go bomb which this plane carries (in-game) was an actual nuclear project by Japan during WW2, though in real life the nuclear program never reached the levels the Manhattan Project did, AKA actually creating a usable bomb.