I got this for my brother and I know it's Japanese, but I don't know the date. Anyone know know Japanese?
It's not Japanese, it's Chinese, Qianlong emperor (1736-1795), Board of Revenue mint. No date on the coin, sometimes these can be narrowed down a bit based on details of how the characters are written but I'm not very good at that. Very common (worth less than a dollar) but still a cool find.
It looks more like a Chinese cash coin. I've ID these before, but don't have the link in my bookmarks currently to get started. If someone doesn't ID soon I'll see if I can at least get a direction for you.... Or we can go with what @Parthicus said....
I think it's an ancient Chinese coin. Check out this link. https://www.calgarycoin.com/reference/china/china8.htm#chien lung In the first image showing two huge coins, yours is the one on the left. Then scroll down and yours is the first one under "Primary Series."