Can somebody help me get there?
First of all, does
God want you to be a missionary in Japan?
Second, are you being a missionary where you are? If you aren't witnessing to people of your own language and culture and leading them to Christ, you will have even greater difficulty doing it overseas.
Thirdly, do other godly people in your church or of your acquaintance believe God is leading you to be a missionary? Are they willing to stand behind you in prayer?
If so, you might start by learning Japanese and studying their culture so you understand how they think. If there are any Japanese in your area, get to know them, learn from them, and be a testimony to them.
Pray! If God wants you in Japan, He will provide a way for you to get there.