Ursula K. Le Guin's Tehanu is the fourth book set in her fantasy world of Earthsea, following the story of Tenar, the main female protagonist, and the wizard Ged.
Like many of Le Guin's books, there are strong feminist themes. She particularly explores the differences between male and female power and magic and the valuable nature of traditionally or stereotypically female traits, actions, and abilities. In this world, women are not allowed to be wizards, and men's abilities and behaviors are seen as superior. Through Ged's loss of power and his subsequent reliance on Tenar for personal growth, we see the shortcomings of wizards (men), who are emotionally immature and concerned with domination, and the power that can come with emotional maturity and a more simple life or more "feminine" ways. It is through his love and understanding of Tenar that Ged is able to find a new, better type of power when he loses his magic.
Additionally, Tehanu, like the other books in the Earthsea series, has Taoist themes. In Taoism, there is a concept called "Wu wei," meaning "non-doing." It involves behaving in a "pure," "natural" way and not disturbing the harmony of the universe by trying to assert one's will over the will of the universe. Taoism values simplicity and detachment from earthly desires. In addition to showing the importance of more traditionally female power, Ged's growth throughout the novel involves moving from someone trying to take action and assert his own will on the universe to someone trying to live in harmony with his feelings and with nature.