How to redeem your DMM Prepaid card
Activate your VPN, and choose an IP in Japan. Sign in with your DMM.com account.
Click on the yellow button with “ポイントをチャージする” written on it, on the right panel.
It will open a new page, scroll down to the bottom of this page.
Type your 10 digits code in the form. Click on the button “使う” and your account will be charged.