9 days in Japan...

Going to Japan for 9 days in mid May. Flying into Tokyo, and spending time also in Kyoto and Osaka. What's your advise on a good itinarary for these 3 places? Is it best to use Tokyo as a base or spend time in each city? Have an interest in castles, theme parks & martial arts, but also open to many suggestions. Your help would be greatly appreicated.

I assume you are flying out of Tokyo?

I would purchase a 7-day JR Pass, activate it on day 3 before you leave Tokyo, so that it is still active on the day you depart Japan.

Kyoto and Osaka are within 30 minutes of each other so you can use either one as your base in the area. It depends what time of year you are travelling and your budget as to which will be better.

It is 3.5 hours or so between Tokyo and Kyoto so I would not do it as a day trip.

I would split time between Osaka/Kyoto and Tokyo depending on interests.

Usually something like first 3 days in Tokyo, then travel to Kyoto/Osaka and spend 4 days in that area, before returning to Tokyo for 2 days before flying home. Some of this depends what time your flights are.

For a castle I'd recommend Hikone which can be a half day trip from Kyoto
http://www.japan-guide.com/e/e7000.html

For theme parks there is Disneyland, and Disneysea in Tokyo. Universal Studios in Osaka, or possibly Fuji-Q Highland in Kawaguchiko
http://www.japan-guide.com/e/e6900.html

There is a Sumo tournament on in Tokyo in May which may interest you.
http://www.buysumotickets.com/Sumo_Calendar.html

There are many useful pages on japan-guide with recommendations on what to see in Osaka, Kyoto, Tokyo and many other cities.

Enjoy your trip!