Since Fakku allows loli, may as well throw this here. Actually, I worked on this a long time ago. However, I'm redoing it from scratch. And knowing me, you should expect something bad.
Pattanko (ぺったんこ) is the Japanese term for a flat-chested female character that is not under age. Manga with this tag will include characters that are obsessive and/or insecure about this fact.