Karashi Also known as Oni Karashi. It is one type of mustard that is used as a popular condiment in Japanese cuisine. Karashi is made from crushed mustard seeds mixed with horseradish and then sold in powder form or in a tube as a squeeze paste. When buying karashi powder, mix it with water for the desired consistency. This is an excellent choice for lovers of oriental spices, especially as karashi mustard is sharper in flavour than, for example, our European mustard. Japanese mustard is most often served with oden, a one-pot nabemono dish that is served in winter due to its high temperature and sharpened flavour. Karashi also tastes great with Japanese natto, a popular fermented soya bean.