I strongly suspect that the book you mention in your explanatory comment was referring (perhaps in a somewhat garbled way) to the notion of kotodama 言霊, particularly as elaborated in the writings of Motoori Norinaga（本居宣長) and other members of the Edo-period kokugaku (国学) movement (often glossed in English as the "National Learning," "Native Studies," or "Nativist" movement).
Kotodama doesn't actually mean "power words," but something more like "the soul of a word," "the spirits of words," or "the spirit of [the Japanese] language." However, the concept of kotodama does ascribe mystical power to certain Japanese words or combinations of words which, when spoken aloud in a ritual setting, were believed to have the ability to alter reality itself. The belief that this power was unique to the Japanese language and made Japan a special land dates all the way back to the ancient poetry collection known as Man'yôshû (万葉集), which was Motoori Norinaga's source for both the term and the concept. And it seems that because this notion of magical power is so central to the concept of kotodama, the term is sometimes (mis)translated into English as "power words".
Many of the nativists' ideas about Japanese uniqueness and superiority – very much including their ideas about kotodama – were quite influential among twentieth-century Japanese nationalists, who adapted them for use in official and unofficial propaganda in the period before and during World War II. (You can read a little bit about how the notion of kotodama informed propaganda and wartime government policy in this blog post by a sociolinguist at Oxford University.) After the end of the war, nativist claims about Japanese superiority were suppressed by the Occupation authorities and critiqued by Japanese intellectuals, and for the most part, these ideas fell out of favor. However, even today there are people in Japan who believe in some version of kotodama.