How can I track my great grandparents who immigrated from China and Japan?

Question:

How can I track my great grandparents who immigrated from China and Japan?

I have Chinese and Japanese origins, and I was told by my grandpa this his dad was Japanese who married a Chinese royal and they were Muslims? The went to Saudi for Hajj and stayed there. How can I track them down? Is it possible that that happened? That a Japanese man marries and Chinese ( who was from royalty?)
Our name was either Yamamuto or Yamatu ...
and the only thing that proves to me that's true, is my grandpa's looks and my family's generation.

Additional Details

6 months ago
My Grandpa died when I was young, and the infromation that I got was mixed up.

6 months ago
since I got really good answers, I'll put it on vote!

Best Answer - Chosen by Asker: 6 months ago
My Grandpa died when I was young, and the infromation that I got was mixed up.