Tokyo weather in October is generally pleasant with daily average temperatures ranging between 22°C (72°F) during the day, and 15°C (59°F) at night. While most days are typically clear or sunny, there is some chance of precipitation. [source]
Momijigari is the Japanese tradition of visiting the autumn-colored trees in particularly scenic areas. The historic town of Nikko is a particularly popular destination for this activity and can be reached within a two-hour train ride from Tokyo.
Tourist activities & events
An overview of upcoming events and tourist activities in Tokyo is available on many websites such as Metropolis.