祈武運長久 kibuunchoukyuu: Prayer for Continuing Success in Battle
忠勇義烈 chuuyuu giretsu: Loyalty, Bravery, and Heroism
The four corners contain the characters: 盡忠奉公 （modern: 尽忠奉公) jinchuu, houkou: Loyalty, Public Service
If we read vertically, 盡奉忠公 it doesn't appear to spell anything.
I would have expected vertical reading, especially given the other vertical inscriptions, but horizontal writing (usually right to left) was sometimes done in the war years and on flags. I also would have expected 盡忠報國, a fixed expression for Loyalty & Patriotism but there is variation in flags.
御嶽教普寛元厷阿講社結社社長清水清吉 This appears to be a name with a title, it may indicate the primary presenter?
御嶽教 ontakekyou (a
shinto sect)
普寛元厷阿? (the name of the organization?)
講社 kousha: religious asociation
結社 kessha: society
社長 shachou: president
清水清吉 Shimizu Seikichi (?): A person's name, but there are many possible readings.
Most or all of the other writing is just signatures.
I believe the name to the left of 祈武運長久 is likely the receiver but I can't read it.
The colors of this flag are extremely well preserved, and the ink oddly shows no signs of discoloration or fading, but it's possibly just a high quality flag with high quality ink provided for the signing along with being well cared for, or at least stored in a beneficial environment. It would be extremely elaborate for a fake, but if you want to be certain you will need to have it examined by an expert (unless someone here finds giveaway red flags that I missed).