How to Ask via email for supervision of professor for Japan Graduate program admission
It needs to be much snappier. Consider something like this:

Dear Professor Name,
Do you have any positions available for graduate students in the Fall? I have a lot of experience with CAD, control systems, and signal processing (i.e., my autonomous underwater robot won the 2018 Singapore competition), and have published a few well-received papers [1,2]. This seems well aligned with your past work on similar topics [3,4], so I would be pleased to discuss opportunities working for you (or your colleagues) as a PhD student. Please let me know.
Name
[1] https://arxiv.org:blah.pdf
[2] etc.

where [1] and [2] are references to papers, links, codebases -- anything they can dive into to understand you more, and [3] and [4] are references to their work, so they see that you took the time to research them.
For me personally, I almost never respond to generic e-mails.
Note, I know nothing about the Japanese system; I'm only commenting on how your e-mail could be generally improved. (In particular, I'm wondering if this mail should be written in Japanese -- I know a lot of science is done in English, but if you speak Japanese, and the language of the university is Japanese, it might be better to write in Japanese or at least provide a translation).