Seidokan Aikido of Tokyo practises every Saturday, 1-3pm, in Itabashi-ku. Classes are free (there is a small charge for use of the sports center), and are held in English. Japanese people with reasonable English listening skill (e.g. toeic 700-ish, or lived abroad for a few months) are also welcome.
The group currently has a good mix of both male and female participants, and a wide range of nationalities.
Beginners are welcome to join on the first Saturday of each month (next beginner day is Saturday, May 2nd).