Keepgo

Keepgo's main draw is prepaid data that doesn't expire, eliminating the rush to use balances before departure dates. Plans cover Japan alongside 150+ other destinations, so leftover data carries to your next trip or next year. This model appeals to frequent travelers and anyone skeptical of traditional use-it-or-lose-it mobile plans.

Buy a Japan data pack in March, use half of it, come back in September with your remaining balance still waiting. That peace of mind costs extra upfront but simplifies repeat travel.