For the package with declared value exceeds 20,000 JPY, the coverage will be different when extra insurance is purchased.

The main shipping method provided at tenso.com is Japan Post and only EMS can choose to purchase extra insurance.

For EMS packages without extra insurance, the max coverage is up to 20,000 JPY if the pacakge is missing or damaged. It's recommended to purchase extra insurance for the package if the declared value is in excess of 20,000 JPY.

About EMS insurance, please check the link below.
https://www.post.japanpost.jp/int/ems/service/damage_en.html