In the past, I would subscribe to the Singtel overseas daily plan when needed. This can range from $15 to $30 depending on the country. In some countries, buying a prepaid SIM works out to be a better deal. Set it up on a mobile WIFI device and the whole family can use the connectivity. Unfortunately, it tends to be used up real fast.
At Changi Airport, a service centre has been set up to provide such services for travellers, both inbound and outbound. I paid $8 for 5 days (special rate with a coupon code from a travel fair) for 6 days of use in Japan, as the first day's charge is waived.
Check it out: https://www.changirecommends.com/owifi.aspx
And if you use this link to make a reservation, I get a $5 voucher for the recommendation: https://www.changirecommends.com/owifi.aspx?rc=if0nn88]
For Japan, the limit was 1 GB daily. 1 GB is a lot for a day. Unless you're surfing video none stop! It sure was handy for my Google Map app on my smartphone as I used it extensively to navigate around in Tokyo and to check which train lines to take and connect to.
I encountered frequent dropped connections on my second day there. Resetting the device seemed to work. I wasn't sure what the reason was. Initially, I thought it occurred whenever there were a lot of strong WIFI signals around. And there are plenty in Tokyo!
But I think the problem was that the battery power drained by the afternoon after several hours of use. Once that happened, it must have gone into a power saving mode. I connected it to a power bank for continuous use. That seemed to work fine thereafter.
Else I would have been completely lost in the maze of Tokyo undergrounds and trains! Happy travels.