I've recently tried out various prepaid SIM cards, and there are quite a few options, so it's a bit confusing. Some can be purchased at convenience stores, while others can't, so you need to choose based on whether you're in a hurry or have some time.

HIS Mobile offers unlimited data for 30 days at around 3,500 yen. It's perfect if you want to use without worrying about data limits. However, it's only available online—no convenience store sales. IIJmio is easy to buy at Lawson and other stores, which is convenient, but honestly, the price is a bit high. The fact that it can be activated immediately is a plus.

Nippon SIM offers a large 50GB plan for just over 4,000 yen. It's easy—just insert and go, with no pre-setup needed. But the speed during the daytime can be a bit unstable. If speed is your priority, JAPAN PREPAID SIM (from Parrot Beak) is better. Since it's directly connected to SoftBank's network, it stays stable at all times.

For temporary return trips or secondary devices, the calendar-world 1-year prepaid plan supports 5G on the Rakuten network. It offers 3GB per month for 12 months at around 6,000 yen. It's cost-effective for long-term use. However, like the others, it's only available online.

If you want to buy immediately at a convenience store, go with IIJmio. For affordability, HIS Mobile is good. For speed stability, JAPAN PREPAID SIM. And for long-term use, calendar-world is a solid choice. Choosing a SIM card depends on your用途, so it's best to organize your usage needs before deciding.