Popotan is a Japanese adult visual novel developed by Petit Ferret with character designs by Watanabe Akio under the alias Poyoyon♡Rock.
The title is a play on the word dandelion, spelled "Tanpopo" in Japanese. The "-tan" dubbed by the Mii - who is the youngest sister, therefore the name is a bit childish and nonsensical.
-excerpts from Wikipedia-
Popotan's DVD-ROM intro was the birth of Caramelldansen.