Good news for anyone looking to join an MMA club in Tokyo even if you don’t speak a word of japanese, there are plenty of options in Tokyo. The one I trained at was Tribe MMA. Located in northeast of Tokyo.
The other one that I considered that seems to have a good facility and reputable trainers is grabaka in shin ochiai.
Otherwise, I will say that training in Japan in general seems to be a bit on the expensive side. I paid almost 11,000 yen a month(about $100) and a 11k yen sign up fee.
The gym I trained at had an english website and all but surprisingly there were barely any foreigners. I was often the only foreigner training or at most another fellow gaijin was at the gym too. This wasn’t a problem though, since training grappling doesn’t require that many words to be spoken, it’s a visual sport anyway.
A funny side note, I met a fellow iranian at the gym which shocked me. Up until that point I had never ran into an iranian gaijin. Unlike me, he actually knew what he was doing, he had been training karate(I think it was) for over a decade before switching over to MMA.
For the training itself, I was pleasantly surprised that it was a relatively moderate pace. I thought being out of shape would make it near difficult to keep it up even in the beginner lesson. I’ve read nightmare stories where some gyms puts such a high pace that newcomers vomit or have to quit in the middle o the lesson. I was tired as fuck by the end of the 1 hour grappling lesson but it wasn’t at the point that I felt I can’t live anymore. Also a big plus, the classes were small(often under 10 people) at the gym I trained.