I am currently stateless.
But this is a good thing. Because Japan does not recognise multiple citizenships, you are required to renounce your existing citizenship as part of the process of becoming a Japanese citizen. If your current countries of citizenship will allow you to renounce those citizenships before you gain Japanese citizenship, you must do so; the Ministry of Justice will not finalise your naturalisation without the document proving that you have renounced your other citizenships. The UK does allow you to renounce your citizenship in anticipation of gaining citizenship of another country, and so I had to.