The subject of this article is a real-life person, place, company, product, or creative work that has been mentioned "in-universe" in InuYasha. The InuYasha Wiki is written from the perspective that all information presented in canon is true; thus, details contained in this article may differ from real world facts.
Lake Sai (西湖, "Saiko") was one of the five lakes around Mount Fuji. When Princess Kaguya is released, the Swallow's Cowrie Shell is cast into Lake Sai to unlock a portion of her power. The element of the lake that Kaguya draws from it is water.