The Wallflower: Yamatonadeshiko Shichihenge(2000)

It's a gorgeous, spacious mansion, and four handsome, fifteen-year-old friends are allowed to live in it for free! There's only one condition—that within three years the guys must transform the owner's wallflower niece into a lady befitting the palace in which they all live! How hard can it be?

Enter Sunako Nakahara, the agoraphobic, horror-movie-loving, pockmark-faced, frizzy-haired, fashion-illiterate recluse who tends to break into explosive nosebleeds whenever she sees anyone attractive. This project is going to take more than our four heroes ever expected: it needs a miracle!

(Source: Del Rey)

Note: Includes the special chapter "Sunako no Otsukai" (スナコのお使い) contained within Volume 5 of the manga.