Need advice on the best way to beat Japanese

So I don’t really play this game competitively and have mostly played single player, but recently I have been playing a friend of mine in 1v1s. The first couple games I was beating him, but then he started playing as the Japanese and just destroyed me. I haven’t won a single game with him as the Japanese. I could have a bigger army or have a bigger economy, but it seems like my army whole always gets wiped out by his samurai. He pretty much spams samurai and trebs doesn’t build many other units. We usually play conquest so no wonders I have to beat him in battle. I usually just do a random civ, but Ive tried the Byzantines a couple times. I think some of the others were the britons, mongols, vikings, ect.. Anyone have advice or tips on countering the Japanese?.