In general, when looking for the cheapest flight to Tokyo, try to choose a flight departing in March for the best deal.
In general, most flyers find the cheapest time to book a flight to Tokyo is about 46 days prior.
From most locations, the cheapest day to fly to Tokyo is Monday. Most users found that departing on a Saturday was most expensive.
On average you can find the best deals on plane tickets to Tokyo when looking for flights with midday departure times.