Let me tell you a bit about the heiresses to the Kingdom of Meresmé...
To be one of the Sun and one of the Moon is one thing, but to be a set of Twins and that? It is rare. As such was conception of twins Annabeth Mariella and Mirabelle Rosemarie. Sun Children and Moon Children are always pitted against one another in nearly everything...and Annabeth and Mirabelle were no exception. For most of their lives, they were forced to fight each other by command of the King and Queen, their parents.
Now, the people of Meresmé are a cruel and vicious people, even to their children, but they hide it well; to them, being that way toughens up their youth. Among the nobles and royals, the children are trained to fight from an early age, as well as in the usual fields befitting future monarchs.
Growing up, the Twins were kept in separate parts of the castle Cavernis: Annabeth being schooled in the Performing Arts and in expanding her mental talents common of Moon Children (she was similar to an Empath in her abilities, but instead of feelings, she picked up memories and thoughts.She has many of the Clair abilities, including clairaudience and clairvoyance, along with being an Intuitive), and Mirabelle being schooled in the Visual Arts and in expanding her talents common of Sun Children (she was an Empath and a Ripper, with the ability to 'rip' through to different dimensions). When they weren't in class, however, they were in the Arena, fighting one another as they were told to do. More often than not, Mirabelle left their Arena sessions with many a near-death experience...
Sun and Moon Children are easy to spot during their respective times by the markings on their forehead: a small red Sun inside of a larger yellow Sun on the forehead and chest on a Sun Child, and a small Full Moon eclipsed by a crescent Moon in the same spots on a Moon Child. The same is true for the Twins. When the Moon comes out, so does the Moon Mark on Annabeth's forehead and chest. When she fights, she shifts into a reptilian form, complete with a tail. Moon Children, however, also have a bloodlust, and it nourishes them (the consumption of blood). Mirabelle has a form, as well--her Sun Form. However, her form is more avian. The Sun Mark on her forehead and chest come out with the Sun as Annabeth's does with the Moon. But it took Mirabelle a very long time to control her emotions and being able to control herself in her Sun Form, resulting in her Sun Mark appearing in the Sun Time. For this reason, Sun and Moon Children usually paired up with their own kind.
In the Twins' case, once the King and Queen learned of a nearby lord who was not only a Moon Child, but an excellent fighter, they wanted to marry their Annabeth to him. However, that lord (Lord Daedna) had a condition of his own: Annabeth had to kill Mirabelle. Her parents accepted his conditions without a second thought, and the two were betrothed shortly after. It was decided on the following Full Moon Rising Ceremony where Annabeth was to dance for her people; by the next Full Moon, they were to be wed... But Annabeth refused to accept his conditions.
She made plans with her brighter Twin to flee; they would leave at dawn through the Gate in Annabeth's Moon Garden. They would only carry with them the necessities that they needed.
They left because their parents gave Annabeth an ultimatem in which she would not comply with---so they went through the Moon Garden Gate and landed on the Durgan Island mainland, Lapavil. But their journey was only just beginning...