Plenty of sunshine, and definitely plenty of runners and spectators. 5th Tokyo Marathon took place on Sunday, February 27th, and I was one on the supporters. A friend from Rhode Island came to run in it, and yes, she finished!!!
The marathon starts at the Tokyo Metropolitan Government building, and you can get there easily from West Tokyo. However, coming back from the finish can take a long time with multiple transfers on the train, and masses of people trying to go home at the same time which means stations and trains are packed. Very daunting to see that many people trying to leave a place. I couldn’t put my runner friend through that after she ran a full marathon. So, I would recommend that you take a taxi from the finish to Tokyo station, and take the Chuo Line from there to get home. The taxi ride was about 2500 yen, well worth the money.