You want a data-only SIM for your laptop in Japan. You're a resident, want to prepay for data, and never want it to expire. Here's the reality and your best solution.
The Japanese prepaid market is built for tourists, not residents with sporadic data needs. Virtually all "prepaid" data comes with a strict, short expiration date. True "non-expiring" data buckets that you can buy and use forever don't exist. But there are smarter alternatives.
7-30
Days Validity
Data is forfeited after the period ends. Inefficient and costly for long-term use.
180-365
Days Validity
A better option, but carries a hidden risk of deactivation if you don't use it regularly.
∞
Effective Validity
A unique monthly plan where data never expires, creating a "data bank" you can use anytime.
Your resident status unlocks two powerful solutions that get you closest to your goal. Let's compare the "Prepaid Bucket" vs. the "Permanent Rollover" model.
Provider Example: Mobile Planning
This model lets you buy a large data bucket (e.g., 20GB) with a long validity period (e.g., 365 days). It feels like a true one-time purchase, but it has one critical, hidden flaw.
The biggest issue is a hidden deactivation clause: if the SIM isn't used for 60 days, it's suspended and you lose all your data.
Provider Example: y.u mobile
This is a unique low-cost monthly plan. All unused data—both your monthly 5GB and any top-ups—rolls over forever, building a data bank up to 100GB. It's the ultimate in data preservation.
With a low monthly fee, you get complete immunity from data loss due to time or inactivity. Your data is always safe.
Comparing a 20GB/365-day prepaid SIM vs. y.u mobile's sign-up with an entry package.
Comparing the price of top-up data between the two models.
This is the most important difference. The prepaid model punishes sporadic use, while the rollover model protects it. This flow chart shows what happens if you don't use your laptop for over two months.
While the prepaid model's one-time cost is tempting, the risk of losing everything makes it a poor choice for truly infrequent use. The y.u mobile plan's small monthly fee is best viewed as a data insurance premium. It guarantees your data is always there when you need it.
For a recurring ¥800/month, you get 5GB of data that rolls over forever, building a secure data bank. This is the most robust, risk-free, and financially sound solution for long-term residents.
If you are strictly against any monthly fee and are confident you will use the data at least once every 60 days, this is your best prepaid option. You must actively manage it to avoid data loss.