Depends on the identification document you have and your choice of pickup location, you can apply from overseas. However, you will not be able to receive the SIM card or Pocket WiFi until you arrive in Japan. We do not ship overseas.
If you have passport and able to pick up the item in person at the Shinjuku office or Narita/Haneda/Kansai airport pickup counters for face-to-face identification verification, then you are more than welcomed to apply from overseas. But please be aware that you will have to receive the item after you arrive in Japan.
Please do contact us if you have further questions regarding this matter.