From Encyclopedia Dramatica
Yotsuba&! is yet another manga series by Kiyohiko Azuma, the same faggot who made Azumanga Daioh. It involves the story of a retarded 4-year old girl who was adopted, then made friends with some next-door neighbors. 4chan is in love with this girl, and asking for any Rule 34 of her will earn you a ban. Newfags will often refer to her as 404 Girl.