There are staff in the rental office. The rental fee for Narita Airport is 1, yen (about RMB 5) a day. You can choose unlimited 3G and limited to 7G/ month. 4G is also available for unlimited use, but it is more expensive.
you must bring a usable credit card and passport when you rent it, and you can pay by credit card or cash when you return it, and you can return it wherever you rent it.
However, if you are still in China, it is suggested that you can rent it on a treasure or at an international airport departing from China. The former is about 1 yuan a day, and the latter is about 4 yuan a day.