What clothes brands does Ayu use?

You're basically looking at any high end designer fashions as far as Ayumi's formal-wear goes. That includes and is not limited to Dior, Chanel, Vuitton, Gucci, Cartier, Versace, Burberry, D&G, and any other brand that you'd see on Fifth Avenue and Rodeo Drive. For daily wear, you're looking at the mid-cost brands such as Guess by Marciano, BAPE, MTRL, 88 Tees, Diesel, etc. Keep in mind that since she is such a big star in Japan, she gets discounts at major department stores and brand flagship stores because she is walking advertisement if she wears their clothing.