Rosa is a tall, young girl with short blond hair and light brown eyes. She wears a gray tank top revealing her navel, brown slacks, and red bandana with her crew's jolly roger on it that matches her father's and siblings'. She is also seen carrying a blue bag.
Unlike her brother and sister, Rosa is not as gullible and, at first, doesn't believe in her father. After he helps defeat Omatsuri and Lily Carnation, she regains her respect for her father and sees him as a hero.
At some point, Rosa's mother died and, later, her father started a pirate crew that consisted of just him and his family. They sailed through the Grand Line, and, along the way, Rosa lost all respect she once had for him as he was shown to be a coward. Eventually, they arrived at Omatsuri Island.
When she was introduced, her father got into a fight with Chopper. After he begged Chopper to pretend to lose to him so his kids would think he is strong in exchange for secrets about the island, Rosa's siblings, Daisy and Rick, believed that their father was strong. Rosa got annoyed by her father, tried to discourage their belief in him, and called him a coward, causing Rick to doubt Papa and disappointing Daisy.
When her father agreed to help Chopper and the Straw Hat Pirates, Rosa found it hard to believe. She later encouraged her father with the help of Luffy to stand up to Baron Omatsuri. After the Baron's defeat she reconciled with her father after seeing his acts of bravery.