魅 is made of 鬼＋未, and 鬼 is from the shape of a dancing man with holding a head of a dead person (so ム might represent a head). 魅 - ウィクショナリー日本語版 鬼 - ウィクショナリー日本語版
On the other hand, katakana ム is from the upper part of a kanji 牟. A famous authority on the origin of Chinese characters 白川静 Shirakawa Shizuka said that this part represents a nose ring of cow. ム - ウィクショナリー日本語版
Thus, the ム in 魅 has nothing to do with katakana ム.