Wasabi Powder is, in theory, a hot-tasting powder made from the dried, ground roots of Wasabi plants.
In practice, however, the pure powders made from actual Wasabi roots are quite expensive, so almost all brands are “fake” Wasabi Powder, actually containing powdered horseradish rather than real wasabi roots, with pale green colouring to imitate the wasabi.
The Hime brand contains: Japanese horseradish, mustard, cornstarch, artificial color, FD&C Yellow #5 (Tartrazine), no gluten. The cans may be labelled “Horseradish Powder.”
You mix Wasabi Powder with some water to form a pale greenish paste. Add a little water at a time to avoid lumps forming, then let stand a few minutes for the flavour to develop. To get it hotter, once you have made the paste, turn the bowl upside down. The paste sticks to the bottom of the bowl; the developing gasses are trapped, making the wasabi paste hotter.
If you are going to be serving it further away than 15 minutes, definitely cover the bowl, or it will weaken exposed to air.
Having Wasabi Powder on hand can be more convenient than buying the pre-mixed tubes of Wasabi Paste, which have a far shorter shelf-life when opened.
Use the paste as a condiment with sushi.
Thin the paste out a lot with some water and some soy sauce and use as a glaze for grilled chicken or fish towards the end of grilling.
Stir a bit into mayonnaise for a zippy sauce for veg.