So... what the hell is a [email protected]? They're basically babies (think Muppet Babies) of the 765Pro idols we know and love, along with their exaggerated traits. Afuu eats onigiri and sleeps slightly more than Miki, Yukipo digs holes -literally- and bursts out in moe goodness like Yuhiko, and Chihyaa bites anyone with ぼいん ぼいん. The only oddity is Haruka's puchidol counterpart, Haruka-san, who multiplies when she comes in contact with water much like a Mogwai.
The anime is based off a 4-koma manga, and the episodes last about as long as reading a couple pages, lasting about a minute outside the ending theme.
As to why these things exist... I don't know. Namco being Namco, I suppose. Funny enough, though, I believe this MAD predicted the arrival of the massive Haruka-san:
matty note: There was also the OVA of [email protected] that was released with Live For You on the Xbox 360 and the three episodes released exclusively on the Shiny Festa PSP games.