Fu (麩 / お麩, Wheat Gluten) is a food made from gluten, the main protein of wheat. It is made by washing wheat flour dough with water until all the starch granules have been removed, leaving the sticky insoluble gluten as an elastic mass which is then cooked before being eaten.
Wheat gluten is an alternative to soybean-based foods such as tofu, which are sometimes used as meat substitutes in Asian, vegetarian, Buddhist, and macrobiotic cuisines. Some types of wheat gluten have a chewy or stringy texture that resembles meat more than other substitutes.
Dried fu above is called Temari Fu (手まり麩), more decorative and fancy wheat gluten from Kyoto area. It’s often used in a Japanese clear soup (osuimono お吸い物). Just throw some into a warm water to hydrate and add to a soup dish.