Alvida was an early One Piece pirate villain- She was grossly obese, but was confident of her 'beauty' nonetheless. Eventually, she ate a demon fruit (fruit with amazing power that change the consumer permanently in various ways) called a Sube Sube fruit. The fruit made her nearly impossible to grab or hold but also caused her to lose weight and actually made her the beauty she always thought she was.
["Sube sube" is an onomonopoetic phrase Japanese use for slippery or extremely smooth items.]
Cluedog/Smooch did a series of pictures on Alvida a few years back. Follow the link since for some reason I couldn't get the preview post to show it properly as the URL was invisible.
http://cluedog.deviantart.com/art/One-Piece-199283054