Sorry, my major is organic synthesis and now is not in Japan. I am not master the detailed information about your field in TIT.
It is hard to say whether the skill of Japanese is a matter, it is case by case. I know there is a lot of Tsinghua student know nothing about Japanese before they went to TIT. So I recommend you to ask the professor directly.
You English is good enough to apply for TIT.
So generally, ask the professor for all the things, that is totally OK.