Title: The Wallflower / Yamato Nadeshiko Shichihenge (volumes 1-8)
Story: Hayakawa Tomoko
Art: Hayakawa Tomoko
Publisher: Del Rey Manga (originally Kodansha)
The person who decided on the English title for this really ought to be caught and put in a small room with no visual or auditory stimulus, there to be confined for an indeterminate period of months. Seriously, though, could you come up with a blander title? Not to mention, it gives absolutely no clue as to the contents of the book.
Anyway, here's the concept. Stop me when you realize just how non-"wallflower" this is.
Four guys are living in a boarding house. One day, their landlady contacts them and says that her niece is going to be living there, and she has a job for them: Make this girl into an outstanding lady. If they do, they continue to live there, at no cost. If they fail, the rent triples. Confident in themselves, the boys agree... But what they couldn't have foreseen was that the girl in question is no mere normal girl. A few tips on grooming and an introduction to polite conversation isn't going to cut it, because ever since the boy she liked called her "ugly", Nakahara Sunako turned into darkness personified.
So, instead of trying their hardest to make a lady out of Sunako, the guys are mostly reduced to attempting to keep the landlady from finding out just how far gone the girl is. Let comedy ensue.
For the most part, this manga can be read out of order. There are few stories that span more than one chapter. Of course, there is ongoing characterization, but it happens at a slow enough pace that it isn't impossible to pick up on it as you go. I would still suggest starting from the beginning, naturally, but if you can't find volume one at your local bookstore, any of the others will serve just as well to introduce you to the story.
The series is currently eleven volumes English-translated, with at least two more due out this year. Meanwhile, the Japanese release is up to volume 18 (as sourced from animenewsnetwork.com), and apparently going strong, since there is currently an anime adaptation ongoing. We can certainly hope that makes its way over here as well.