The large kanji on the left side are 加茂君平君. 加茂君平 Kamo Kunpei is the name of the recipient of the flag (君 kun at the end is a title).
You got the meaning of the slogan at the right side correctly, but it's actually 祈武運長久 Inoru buun chōkyū. As you can see, there are 5 kanji there, and the second kanji is "bu", not "bun". Also note that long vowels and short vowels are strictly distinguished in Japanese. The last two kanji are both long vowels.