Had some time, so i did a short bike tour when i was in Tokyo. A relaxing 3 hour ride in 20+ degrees. I must say that it was fun, safe and something i would recommend especially wifi you enjoy cycling. Granted that the other routes that are 6 hours long might offer a little more variety, but if you have just half a day, it is totally worth it.
Bike route, photos and some brochures that i picked up along the way below.