Should i get a speedo for Japan?
If you are not Japanese or of another culture that can easily blend in, then why try to? It will be clear you are an American (I’m assuming) so just wear whatever you are comfortable with. I seriously doubt anyone there would think you were weird for doing so. That being said, if you feel like trying speedos, why not?! It certainly is a more-accepting place to do something like that than here in the states. So do as others have said and pack a pair of trunks, and then a speedo if you are really set on trying it. Keep in mind you could always buy a speedo while in Japan as they probably have them everywhere if they are so dominant there.