PROTIP: Other than becoming a terrorist, it is extremely hard to get rid of US citizenship. I would say it is much, much harder to get rid of US citizenship than it is to get it. The USA is the only country in the world that still requires you to pay taxes even if you are a US citizen but don't live in the USA.

Also, you can't become japanese other than changing your DNA and becoming japanese. They don't award citizenship for being born in japan, you have to have japanese blood.