It is extreme;y difficult to change one's name in Japan. It takes years in court, a lot of money, and a good reason. What's more it is very impractical as you have to get all your documents (diploma, passport, bank cards, registrations, member cards, work or accommodation contracts, etc.) renewed, by explaining them you changed name, and as it is very unusual in Japan, it may take some time and trouble. The same is true for most continental European countries. In the UK however, it is even easier than in the States thanks to the 'deed poll'.