Cottontail is one of Peter's sisters and one of the three tritagonists in Peter Rabbit.
She is a very pale brown bunny, and also the youngest with a green shirt and brown eyes
She is described as “the loose cannon” by Daisy Ridley. She's paranoid, feisty and headstrong.
Little is known about Cottontail's early life
Cottontail, her sisters, Peter and Benjamin spend most of their days picking on Mr. McGregor and stealing his vegetables from his garden. They are friends with a local woman named Bea who spends her time painting pictures of the rabbits as well as the surrounding nature. Peter invites all of the woodland critters and then takes over McGregor's old house. When Thomas kicks out Peter and his friends and begins to secretly wall up to the garden, despite Bea's objections.
Peter and his friends use their tricks to kick the couple out of the house.
During the end credits, it is shown that Bea, Thomas, and the rabbits eventually moved to London together where Thomas has his own toy shop and Bea begins to write and illustrate books based on Peter and his friends.