When accidents happen
When you are in an accident.
Things to know are...
Was anyone hurt?
Did you damage someone else property?
Know your insurance before hand. The police in Japan will not help you, they will only do their job. Which is take record of the accident, they won't tell you who's fault is was. That's not their job.
It would be wise to get insurance from an insurance company that talks English.
Make sure your insurance company and the other person's insurance company talk.
Let them take care of the negotiation.
As for the driver you will be asked questions to fill out a report.
Also they will ask you to go to the police station.
Make sure you have your passport or alien registration card.
They will follow you home if you don't have it with you.