I am not sure of the meaning of BBQ, but I hope this restaurant would be suitable for you! The dinner is a bit expensive so I often go to having a lunch.
Maybe you are looking for the restaurant like this?
The English menu shows only regular food.
But they serve all you can eat crab BBQ in this season.（You can check it in Japanese website ）2 orders minimum though....
or you can eat crab in hotel buffet.
Almost hotel buffet offer crabs in this season.Of course, for 1 person.