Taxi Prices in Tokyo
Taxi prices in Japan are controlled. In Tokyo, they all start at 710 yen for the first 2 km. The price rises at a defined amount, either by distance or time. If there is no traffic, the factor that will trigger a price rise is distance traveled. In traffic, the factor is time. Either way, the cost will be the same in every taxi, no matter the company or even an independent operator.
In addition, there is no tipping of taxis in Japan. Most drivers will not only not accept a tip, but they will have no concept of tipping. It usually isn't worth trying.
What this means, then, is that riding a taxi is a very low-risk service. There is nearly no situation in which a Japanese taxi driver will negotiate on the ride. You will never get a special deal; nor will you be "taken for a ride." Well, except wherever it is that you want to go. :-)