Japanese ōen pennant — a cheering pennant, the kind given to encourage.

According to my ai assisted research,

It reads top to bottom: 奮起必勝 (funki hisshō) — "Rouse yourself to action; victory is certain." Basically "give it everything, you're going to win."

It may be and say something else entirely so please use your judgement.

Looks older, ww2 perhaps?

Please see pictures as they are part of the description.