Japanese WWII Flag: Authentic or Fake?

Hello everyone, I'm posting a picture of a flag my uncle has. My apologies for the glare as you can tell it's behind glass. The story is that my grandfather obtained this flag overseas in WWII. How he obtained it I'm not sure. I was just hoping to get some feedback from some of the members on weather or not it's look like an authentic "Good Luck" flag or one of the many fakes. I obviously don't read or speak Japanese so any info would be appreciated. Thank you in advance.

Tried to make it a bit more readable for our helpers.

Addressed to Tsutsumi Kinjirō (other readings of the name are possible). At the top it says "congratulations on joining (the military".
Down the right side it says "pray for everlasting military luck". Hard to say if its authentic.

Alright, cool. I appreciate it.