Ninja Asakusa Reservations

My family and I really want to go to the Ninja restaurant in Asakusa while in Tokyo next month. They use the Opentable reservation system. Even over a month in advance, there seems to be no tables available at pretty much any date/time I try to reserve seats. Does anyone know if they perhaps no longer use Opentable and only take reservations by phone now? If so, is there any chance they will have an English speaker available? If we can't get reservations, what are the wait times like? TIA!

Note that it is in Akasaka, not Asakusa.

I get the feeling that they discontinued using opentable or allocate only a small number of tables to the system which book out quickly.

As you probably have seen, they are also having their own reservation form on their website:
http://www.ninjaakasaka.com/yoyaku/form.html

If you don't want to try calling by phone, I recommend to try it through that form.

Thank you! I knew it was Akasaka, don't know why I typed Asakusa. Not only that, I didn't actually see the reservation form on their website, so thank you very much for the info!