Mustangs were pretty rare in the Pacific war. Frankly, with only the one picture, it is hard to tell. They say it is upside down, but the angle of the connection of the wing to the fuselage strongly implies both that it is upright, and that the wing attached to the top section of the fuselage.
The plane is not very big, but it seems to be pretty wide compared to the boater.
Look closely.
The engine and prop has broken off from the main fuselage and fallen down at an angle.
The wing flaps are pointed ‘down’, which means they were ‘up’ when it was crashing. The pilot was desperately trying to gain altitude or intentionally stalling trying for a ‘soft’ crash in the water....................
Mustangs didn’t come into play until late in the war. They primarily flew long range B 29 escort missions from Iwo. B 29s from Tinian. Later when 29’s shifted to night missions the 51’s changed to ground attack role on Japan proper.
This plane is not a 51. It is not upside down. High wing monoplane with what looks like a rather long greenhouse with what could be a rearward firing machine gun , Flaps are down and appear perforated like dauntlass dive brakes.Appears to be a single radial engine that has partially broken off downward. Its not a dauntless. More likely Japanese of some sort.
After writing this I did more research and found they are saying its a TBM Avenger.