Running is a very popular sport in Japan and the Tokyo Marathon is hugely oversubscribed at registration time (usually in August).
But even if you are not running the event, there’s a festive atmosphere along the course so it’s worth checking out. Good places to watch are near the starting point: the Tokyo Metropolitan Government Building in Shinjuku, near Tokyo Station where the race finishes, or in Ginza where you can combine viewing with some shopping—but wherever you watch it from, expect crowds.
This year, there will be 38,000 runners—37,500 for the marathon and 500 for the 10km race. The event starts with the wheelchair marathon and 10km at 9.05 am, followed by the marathon and 10km starting at 9.10 am. The 10km races are due to end at 10.50 am and the marathon at 4.10 pm.
Note that although watching the race is free, entering is not—the marathon costs ¥16,200 yen for Japanese residents and ¥18,200 for foreigners, while the 10km costs ¥5,600 for Japanese residents and ¥6,700 for foreigners.