ByteSIM offers unlimited data eSIM plans for Japan through its 5G Ultra Unlimited eSIM by KDDI. These plans have a validity range of 4 days to 31 days and a price range from $18.90 USD to $79.90 USD. They provide 4G and 5G coverage and include tethering; however, speeds may be throttled after heavy usage under the Fair Usage Policy.
If you are concerned about potential speed restrictions, it is advisable to contact ByteSIM directly to confirm whether a Fair Usage Policy applies and to learn the typical amount of data available at normal speed.