Konnichiwa Mikemike88-san! Majestic-sam!
I can't tell whether this flag is real or not. The only thing that bothers me is that there is no dot in the upper right corner of the large character "武".
The name "林武俊" is written in the lower center of the flag. This name also uses the same character "武", but with a dot in the upper right corner.
This is a kanji character that no Japanese person would mistake. There is a person who use the same kanji "武", then it's all the more strange that large character is wrong.
There is a misunderstanding regarding the term "義勇奉公", so I will explain. "義勇" means justice and courage, and "奉公" means "dedication". In this context, "義勇奉公" means dedicating oneself to the nation and fighting bravely. This is a word that was commonly used before the war, but is no longer used today.
Incidentally, adding "兵:soldier" to the word "義勇" does not mean "soldier who fight bravely." "義勇兵" means "volunteer soldier". "volunteer Army" is "義勇軍" and is not mean "bravely Army". Despite the word "義勇" being included... Japanese is very complicated...
There is another message hidden within this flag. It's written "奮闘ヲ祈" where is next to the name "林武俊," It means "Good luck!"
NANGI