The flag has patriotic slogans and various invocations of martial virtue.
"Build a strong country"
"Japanese (Yamato) Spirit!"
I couldn't find the name of the owner, but there are several names of people who signed the flag (Sasaki, Matsushiro, Takahashi, Hayasaka, Hatake, etc.). There are also the words "Miyagino Spirit" to the left of the red/sun circle, which most likely indicates the place of origin: Miyagino-ward (in the city of Sendai, a few hundred kilometers north of Tokyo)