Sienna is a beautiful and elegant businesswoman who owns Phantom Isle, Marona's home. She is generous and polite to a fault, but her calm demeanor holds a few secrets. Even her assistant, Murasaki, is clueless as to Sienna's true motivations, or what it is about Phantom Isle that makes it so important to her. Besides Phantom Isle, Sienna owns an immense Bottle Mail factory. It is later revealed that she was the legendary hero Scarlet the Brave before she was severely wounded in her battle with Sulphur, and that she gave up being a famed warrior to live a calm life of relative obscurity.