Call China from Japan to buy a domestic card by mobile phone or landline (500 minutes on Taobao will be normal).

Call a Japanese mobile phone from China to buy an international card (very expensive. Taobao 95 yuan can buy 10 Euro, and the face value of 1.25 Euro will be used up in one minute. . . . ) or a domestic card (if you dial 1 minute with different dialing methods, the domestic card will lose 12 minutes instead of 13 minutes, and the average price of 1 minute is cheaper than that of the international card).