Meluzina Undina is a character appearing in TYPE-MOON's Fate series (especially Fate/Grand Order), with her core identity being the fairy knight Lancelot, and she is also connected to European legends of fairies and water spirits. Her real name, Melusine, comes from a French folk tale. She is the heroine of the "Interspecies Marriage" story, born to a human father and a fairy mother. As a half-human, half-demon beauty, she has a unique appearance with a snake tail and dragon wings. Because she was accused of imprisoning her father in a cave, she is cursed to "turn her lower body into a snake every Saturday." Legend has it that if her lover witnesses this form, the curse will intensify and permanently transform her into a terrifying serpent. "Undina" is related to the legend of the water spirits, one of Europe's four elemental spirits. These spirits must marry mortal men to gain souls, and if betrayed, they return to the water and lose their souls. This setting fits with her storyline, where she is given life by Aurora, and later requires the Master to grant a new soul due to related experiences. In terms of character design, she is one of the Knights of the Round Table in the fairy kingdom of Britain, known by titles such as "Descendants of Albion" and "Britain's Strongest Knight on the Lake." She has a cleanliness obsession and tense atmosphere. Although she is seen as a "cold fairy," she does not reject or hate humans and cherishes "the gentle comfort of the weak." She possesses the B-level "Dragon Heart" skill, with a magic circuit like the Dragon's Furnace, possessing dragon-like biological abilities; B-rank "Infinite Martial Training" skill originates from the Heroic Spirit Lancelot, allowing him to exert full power in any mental state, but he dislikes this skill due to his innate toughness; The A-rank "Horizon of Light" skill originates from the legend of the dragon guarding the Gate of Another World, revealing that she is essentially the vessel of the "Realm" itself. Additionally, she has the image of "Swimsuit Melusin," appearing as a Ruler-class swimsuit model, showing a cute and lively aura beyond the norm. She wields the weapon "Melufistdight Innocence" and pairs it with interchangeable parts for a variety of poses.