You can install the eSIM outside of Japan.

However, it is strongly recommended that you install the eSIM after you arrive in Japan for the following two reasons.

Reason 1) We sometimes see occasional errors when the eSIM profile is installed outside of Japan.

Below is a few examples of reported errors.

※These errors appear due to the eSIM being installed outside of Japan. Usually, you can still use the eSIM normally after you arrive in Japan and turn ON the eSIM. Please do not rush into deleting the eSIM.

iPhone: 

"Unable to Activate eSIM" message.

eSIM gets stuck on "Activating ..."

Android phones:

It does not give you an error message, but there will be no signal bars displayed.

Reason 2) Regardless of the usage period that you entered at checkout, your eSIM's usage period will begin when you install the eSIM onto your device.

Therefore, if you install the eSIM before arriving in Japan, your eSIM can expire earlier than your intended last date.

If you installed the eSIM outside of Japan, and you are not able to use the data after arriving in Japan, please see here for more troubleshooting tips:

eSIM installation trouble shooting (Travel eSIM)