Casilda

Casilda (or Princess Casilda), also known as Princess Marina's Gargantuan Form, is an alternate form taking the shape of a strong teenage princess, who is also a strong fighter and can use some magical techniques. It is currently the oldest alternate form of Marina. This form contains the princess's spirit.

Background
During the ancient times, there was a cheerful teenage princess named Princess Casilda who rule over her kingdom with her younger brother, the prince. She was known as the Gargantuan Princess, due to her large appetite as well. But that made her very strong. There was a war in the kingdom, causing the loss of her parents. The young brother had lost his voice, and the next queen of her kingdom went on an adventure to search for a potion and avenge her parents by defeating the causer of the war. She found that potion and then healed her younger brother, and the kingdom was finally at peace, thanks to her bravery. Finally, Casilda became the queen of her kingdom. However, the queen's fate was unknown, implied to have lost her spirit.

Casilda Reborn
Eventually, Casilda let her spirit rest within Marina, the princess of Sea Side, allowing her to be able to transform in her Gargantuan Form as Casilda. By accident, she already proven her true identity as Marina, which made everyone on Sea Side to be able to recognize Marina, especially her father and her mother and the rest. Eventually, her Gargantuan form became one of her favorite alternate form she uses the most like her Young Form.

Trivia

 * Casilda is a character based on Tia from Zatch Bell!.
 * Casilda is the form that Marina possessed several years ago prior the events of Sea Side Adventure, at least some unknown amount of time before the events of Invasion of Sea Side. Despite being about twenty years before Sea Side Adventure, Casilda Marina didn't shown a sign of aging. It should be noted that Marina no longer ages, especially in her alternate forms.