メトロ電気株式会社 （ Metro Electric Co.,Ltd. ） only takes Cash on Delivery and Bank Transfers, notably only from Japanese banks, and is thus not advisable for international purchasing.
Direct fulfillment from Sensatec international fulfillment (English site) uses flat rate shipping fees for EMS as determined here:
Depending on current conversion rates it may be advisable to use other currencies provided you can avoid foreign transaction fees with your payment provider, as Sensatec does not use current conversion rates for USD and EUR.
Sensatec domestic deliveries to Japanese addresses are only accepted through the Japanese site (https://www.sensatec.co.jp/) and are subject to 10% consumption tax and it only accepts JPY. As such it may be advisable for small orders (2 pots) where you can use a mailforwarding service, but when ordering multiple the 10% consumption tax outstrips the flat rate EMS shipping.