Kyodo News reports on the matter

The report says that the government plans to introduce vaccine passports in order to make it easier for people who have been vaccinated against COVID-19 to travel internationally, citing government sources on the matter.

Adding that the vaccine passports are anticipated to come in the form of a smartphone app, using QR code scanning when boarding a flight or when entering the country.

I reckon we are still some ways off from this coming to fruition but it is arguably the next step that most countries will be adhering to when they start to reopen for travel.