Daphne is Bloom's older sister, and the eldest daughter of King Oritel and Queen Marion of the recently resurrected world, Domino. She was also the last fairy to have acquired the great sea/ocean-themed transformation and power of Sirenix.
She was/is the spirit of an extremely powerful nymph, bound to the bottom of Lake Roccaluce in Magix, as she was killed sixteen years before the beginning of the events of the show when the three Ancestral Witches destroyed her world and its inhabitants and returned to Domino after it was successfully ressurected and reborn in The Secret of the Lost Kingdom movie.
In the first Winx movie, Daphne demonstrates her resourcefulness: solving Bloom's problem with finding the secret Domino library by giving Bloom her mask. With it, Bloom would be seeing through Daphne's eyes and see Domino as she remembered it before it was obliterated.
Despite the fact that there is a constant aura of mystery and secrets about her, Daphne was a kind and loving woman, and an utterly devoted sister to Bloom (she willingly sacrificed herself for her younger sister), to whom she acts as a guardian spirit of sorts, guiding her through her troubles with both her magic and adventures, telepathically communicating with Bloom if she has any trouble.
Daphne's age remains a mystery, though it is known she was either a young adult or a teenager at the time of her death (due to examination of her pictures from the Book of Destiny in the first movie). Along with her age, Daphne's upbringing and her fairy form are mysterious even if she has been seen to be powerful enough to fly without wings, although that could be because she was a Nymph (however it was never precised whether Nymph is a fairy form or just a title).
Daphne is not quite emotionless, though often she is portrayed as serious. This is due to the fact that she is only seen during more dire situations. Although, in the second movie, Daphne reveals her more playful side as she jokingly acts as a ghost scaring Bloom and in most of the appearances she made she was quite cheerful and was smiling. In Magical Adventure after Bloom frees a fish she was forced to eat, Daphne appears and tells Bloom that when she was alive she also had to eat raw fish and that it tasted horrible.
In the fifth season, when Bloom asks about the location of the ancient Book of Sirenix to Daphne, she is seen losing her calm demeanor out of concern for her little sister, since the dark spell that the Ancestral Witches had placed on Sirenix caused her to become a disembodied spirit without a physical body of solid flesh and blood.
In the fifth season finale, Bloom had used her Sirenix wish to have Daphne fully restored to her physical body at last. Daphne and Bloom finally shared their warmly, sisterly embrace, finally able to touch each other. This means that Daphne is finally free to live on her home world with her parents - Oritel and Miriam - and younger sister at last. She is no longer bound to Lake Roccaluce or the source of Sirenix.
Daphne has white skin, long burnt-blond hair and brown eyes. She is also notably shorter than she was in her nymph form.
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Nymph of Magix Edit
According to the RAI version of Winx Club, Daphne was one of the Nine Nymphs of the Magical Dimension: nine all-powerful fairies that, after the disappearance of the Great Dragon, controlled the destiny of the Magical Dimension. She was in fact the Supreme Nymph of Magix, being the last and most powerful one among them before Domino's destruction and the disappearance of the Dragon Flame. She was apparently a tremendously strong and powerful fairy when she was the keeper of the Dragon Flame. since in "Betrayed!" of the first season; Bloom tells Sky that she first saw Daphne on the walls of a temple found at Magix, along with the other Nymphs of Magix, and there was a statue of her in the Museum of Magix.