Given a travel related situation, and given a specific question about the situation, summarize the question into a title
Q: Is it acceptable to show up unannounced to a car rental shop and rent a car for ~5 days? Is it better to reserve in advance via a website?

I speak decent japanese and should be able to explain the situation and understand details.

General answers are prefered so the question can be of use to more people, but my particular situation is such:

Short delay (next day)
Greater Tokyo area

A:
In Japan, should rental cars be reserved in advance?