It wasn’t uncommon to open your canopy to get a better view, I don’t know what to tell you besides watch some old dogfight interviews.

The Soviets were practically infamous for always flying with them open. Not unreasonable to think a pilot that considered combat over might open his canopy.

And, also, sucks to suck. War crime protections are agreements between nations on standards of behavior, and Imperial Japan violated them all, so even if it was:

Good, fuck that fash.