She’s a member of Faerie Britain's Knights of the Round Table. She is a Fairy Knight assuming the name of the Heroic Spirit Lancelot, who belongs to the Greater Human History's Knights of the Round Table. The sole "dragon" species fairy in Britain. She acts in the manner of a merciless knight, but because of that conduct, her elegance and her appearance that distinguishes her from other fairies, she is said to be the proudest and most beautiful of them all.
She is the left hand of the Dragon of Albion which fell off the dragon's rotting corpse and eventually evolved to have a humanoid form before Aurora came and adopted her, given her the name "Melusine". Melusine was destined to become the Calamity of Flame, Albion, but Aurora giving her a name managed to stave off the transformation. Unfortunately, this made her indebted to Aurora, whose continued existence would allow her to remain as "Melusine". All it would take is Aurora's death for her to return to Albion, which could happen as much from random chance, Aurora losing her purpose and fading or becoming a Mors.
Melusine claims she is the older sister of Percival. Percival says that they were raised and trained together.