The Japanese generally do not like change of any kind.
Why don’t you rent for a longer period and find out if there is a charge to return the car early.
Any sudden extensions will generally result in a higher fee, and also impossible to to rent the car for longer because they have promised the car to someone else the next day. Think about if you ran a rental car business, what would you do?
Even if I taught you the JP expression, you might not be able to understand their response.
Best of luck,
It all depends what you mean by “last minute”. The rental companies allow extensions, and they’ll be as flexible as they can be, but my advice would be if you want to extend your rental, make sure you can still return the car if the rental company says no. So don’t call 2 hours before the return when you’re 5 hours drive away.
I have asked for an extension the day before the return date from a different company and it was fine. There is a small fee for extending but it’s not an unreasonable amount.
jrtokyo is trying to be helpful, but “the Japanese generally do not like change of any kind” is a bit inaccurate. Most big companies with a mass market are quite flexible. There will be fees for changes, but that’s pretty normal. The rental car offices do keep small inventories though, so as jrtokyo says, if they’ve already rented your car out the next day, you won’t be able to get an extension. If your can’t extend the rental on your car, you might be able to get a different car from the same company - either bigger or smaller.