Plain yogurt (dahi, curd) in Japan: what it's called and where to buy it
Unsweetened yogurt is プレーンヨーグルト in 400 g tubs. Check for 無糖 so you get the one without sugar.
Look for this on the label
プレーンヨーグルト
purēn yōguruto · plain
無糖
mutō · no sugar
ギリシャヨーグルト
girisha yōguruto · Greek, thick