i have posted a review of the flag book. one person who bought it said he would like more historical context on slogans. I agree with this. there are some sayings in other countrys that only they can understand a culture thing. for that reason this flag was strange it has the slogan "DRAGON and TIGER: TWO MIGHTY RIVALS". I know both animals are significant in Japanese culture. why rivals? i personally have never heard this saying does it have cultural significance. assuming the flag is real.
It literally only says "dragon & tiger" (龍虎). The two mighty rivals thing comes from a dictionary (I see it in the EDICT entry). In other words, it could be translated that way depending on the context. In this context I would guess it's just a phrase telling the soldier to be strong and to persevere like the two strongest animals in mythology.
Here are some notes about the meaning of dragon/tiger in Chinese mythology. I imagine the Japanese meaning is more or less the same. There's a wikipedia page on it but it doesn't really say much.
The section on the lower right is from some "11th" Imperial Military group in Asahikawa city (Hokkaido).