pixiv-tan is a semi official mascot character for the illustration community web service pixiv.
pixiv-tan is considered to be an official personification of pixiv itself. Since pixiv has no official design (the design is completely up to the person who partakes the annual contest), the character cannot be considered as an image character, or mascot character.
However, users who participate in the design usually draw her with blue and white colors, since those represent the direction of the website, and the color of the logo. She is usually seen to hold brush, pen or digital tablet pen in most artworks.
pixiv-tan is proven to be popular and is sometimes considered an idol that represents the site, usually drawn as a young female or even a child (if one were to go by age of the site). While people can draw pixiv-tan anytime they want, the submissions of her increase during September due to the anniversary of the site, as well as the annual "Let's Draw pixiv-tan" event held by the staffs of the site. Aside from official projects, the staffs also released fully pixiv-tan-centric books named "pixiv-tan Artwork Collections". Different volumes of the book are available exclusively at different times during Winter Comiket.
On the 4th official event, to celebrate the expansion of pixiv to users worldwide, the project included events in which various artists drew pixiv-tan with different races and in national costumes of different countries.
pixiv-tan Plus Future
pixiv-tan Plus Present
pixiv-tan Plus Past
pixiv-tan Plus Other Dimension
White One Piece