/ani/-tan's simple looks reflect its personality: it's a lazy person, with little to no worries or cares in its life. The one thing it cares about is getting laid. Because of this, it'll frequent drawthreads on various other boards and encourage people to make animations, as fellow shapeshifters are more interesting than just playing with itself no matter what form it takes. It's also a familiar face at the yearly interboard Superbowl party, but again it's not in it so much for the game as for a chance to get its doodle wet.
/ani/-tan started out as an avatar of the board owner of the eponymous board, who used it to interact with other drawfags in the past. The board owner has since come to regret these actions, so maybe the current /ani/-tan is a bit more mature than the one described here.