It's addressed to a Mr./Professor/Doctor Hosoda (Hosoda is a fairly common Japanese surname). There is a date down the left side that says September 7th 1942. The line next to that is from the group that presented the flag to Mr. Hosoda, and I can't quite read it but it looks like it might be the name of a hospital. Across the top of the flag is 武運長久 (Good luck in battle). Along the bottom are the names of well-wishers for Mr. Hosoda.
Hard to say if its real or not. It isn't the most convincing flag I've seen. Possible to get a better shot of the vertical line in the middle of the far left side?