The short answer
A pocket Wi-Fi is one rented router that several devices share; an eSIM is a digital SIM on each phone, so the number of people in your party decides most of this. Japan is unusual here: renting a pocket Wi-Fi is a long-standing habit for visitors, and the rental counters at the airports exist because plenty of people still do it. For a family or a group that moves together, one device can be the cheapest way to keep everyone online. For a solo traveller or a couple, and for anyone who splits up during the day, an eSIM is simpler: nothing to collect, carry, charge or return.
How pocket Wi-Fi rental works in Japan
You book the device online before the trip, collect it from a rental counter at the airport when you land, use it as a shared hotspot, and hand it back before you fly home. This is a genuinely established way to travel in Japan, not a fringe option, and the counters are part of the arrivals routine for a lot of visitors. The unit is a small battery-powered router: you switch it on, everyone joins its network, and one data plan covers the whole party. The obligations come with it. You are responsible for the hardware, you have to be at the airport in time to return it, and you carry a charger for it alongside your own.
The eSIM by comparison
An eSIM is per phone: you install it from a code before you leave home, switch it on when you land, and there is nothing physical in the transaction at all. No counter at arrivals, no deposit, no device to lose, no return deadline on your last morning, and your home number stays live for calls and bank codes. The limit is the same coin's other side: an eSIM covers one phone, so four travellers need four of them, and each person's data is their own. Goodbars sells a Japan eSIM you install at home and switch on when you land; it runs on NTT docomo, Japan's largest mobile network by mobile contracts, and our Japan coverage page shows where it reaches and what independent speed tests measure. Your phone does need to support eSIM, which most models from recent years do, and it must not be network-locked.
One device, one battery, one point of failure
The practical catch with a shared router is that everybody depends on one gadget with one battery. Someone has to carry it, remember to charge it overnight, and stay within range of everyone else. In Japan that last part bites more than you would expect, because people split up constantly: one goes to a shrine at dawn, one queues for a ticket, one heads back to the hotel with the shopping, and only the person holding the box still has data. A flat battery in the afternoon puts the whole group offline at once, and a device left on a train is both an outage and a bill.
Cost per head, and who should choose which
On money alone, one shared rental splits across several people, so a group can pay less per head than the same group buying separate eSIMs. That arithmetic flips fast as the group shrinks: a solo traveller carries the whole rental alone and almost always does better with an eSIM. So: choose a pocket Wi-Fi if you are a family or a group that genuinely moves together all day and wants one bill. Choose an eSIM if you are solo or a couple, if your group splits up, or if you would simply rather not add a collection and a return to a trip that already has trains to catch.
