Leen is an ancient fairy, over six hundred years old, who belongs to the fairy tribe of the Kingdom of Mismede. She serves as the tribal elder and formerly held the position of court mage for the kingdom, later becoming the court magician of the Brunhild Dukedom and one of Touya Mochizuki’s spouses. Despite her great age, she retains the youthful appearance characteristic of fairies, with white hair that falls to shoulder length, golden or orange eyes, and a pair of wings that she often conceals using light magic when in public. She is frequently accompanied by a teddy bear named Paula or Bolla, which she animates and controls with her unique null‑attribute magic called Program.

Leen is a remarkably skilled magician who has mastered all six of the major magical elements except for dark‑attribute sorcery. Her command of magic is so extensive that she can use non‑elemental spells such as Transfer, Protection, and Discovery. Her personality is marked by a playful, often mischievous streak; she has a tendency to act out of spite and takes a certain sadistic pleasure in provoking reactions from others, though this behavior is balanced by a genuine sense of responsibility and loyalty to her allies.

Her primary motivation is to protect her people and support the kingdom she serves, and she later dedicates herself to aiding Touya in his endeavors. She develops a close bond with Touya, whom she marries, and interacts warmly with his other wives. Throughout the series, she remains a steadfast magical expert whose centuries of experience prove invaluable in both combat and diplomatic situations. Her growth is shown in her gradual willingness to let go of her aloof demeanor and embrace her role within Touya’s growing family, all while continuing to wield her vast magical abilities to solve crises and defend those she cares about.