Your question is quite broad in scope so hard to nail it down
Depending on the time of rental.
1) buying a cheap computer would be cheaper for a rental of any duration
2) Some video/game shops do this, as well as rent software.
3) FREE is better: many cities have community and international centers where you can use a computer on site for free. Most libraries (that I have visited) do as well.
4) Visiting/travel - Many business hotels have a business center - free computer use (which I have never seen anyone use because I do not think a Japanese business person exists that does not have a PC and or smart phone/ Tablet)
5) Some business hotels that I have stayed at even have "free loans of a notebook to guests).