TOKYO -- When Mayumi Yamamoto goes out for coffee or window shopping, she likes to look as though she's going to a formal garden party. One day recently, she was decked out in a frilly, rose-patterned dress, matching pink heels with a ribbon and a huge pink bow atop her long hair, dyed brown and in pre-Raphaelite curls.

Ms. Yamamoto is a hime gyaru, or princess girl, a growing new tribe of Japanese women who aim to look like sugarcoated, 21st-century versions of old-style European royalty. They idolize Marie Antoinette and...