Erotic Juice BE (Henmaru Machino Translated Manga) (Warning: Incest)

This is an English-translated short story from Henmaru Machino, a bizarre hentai artist that I like very much. This is one of his most 'normal' stories: an big brother and his younger sister having an incestous relationship begin drinking an unlabeled juice from a vending machine that mysteriously appeared near their house. The juice ends up being an aphrodisiac, and as a side-effect it causes the girl's breasts to gradually grow through-out the manga.

The torrent with the entire book of translated short stories can be found
here: http://www.deadfrog.us/index.php?act=entry&id=6695
Be warned, however: There's tons of weird shit in this volume, with an emphasis on beastiality and body-morphing. It's so completely out-there, however, that you might find it fasinating.

EDIT: OK, this may not be incest after all: Onii-chan is sometimes used out of the context of the meaning 'brother'. But I doubt it, since it's other meanings (a young man of older age or social standing) are meant for a formal context, and the addition of -chan is meant to be familiar/affectionate in nature. I'm just nit-picking now.