I would just suggest having the flag of the Imperial Japanese Army in the canton of a pure gold/yellow flag.
I dunno, this design caught my eye:![]()
The third flag looks great, with the red border.
With the Soviets collapsing into civil war in Siberia, I wonder if it would be possible for Mengjiang to have conquered Communist Mongolia. At this point the Soviets most likely will withdraw there forces to deal with the rebellions in Siberia. The Kwantung army, while weakened could still beat Mongolia. In 44 or 45 Japan could have exploited Soviet collapse to expand their influence in Asia. They already occupied the far east, so what's stopping Japan from conquering Mongolia?