Lantis is a powerful magic swordsman known as a Kail or Cail who first appears in the second part of Magic Knight Rayearth. He is the younger brother of Zagato, the former High Priest of Cephiro, and once served as Princess Emeraude's captain of the guard. After sensing the forbidden love between his brother and the princess and foreseeing the tragedy it would bring, he left Cephiro and traveled to many other worlds, spending considerable time on the planet Autozam. His return to Cephiro occurs shortly after the death of the previous Pillar, Emeraude, and the defeat of his brother at the hands of the three Magic Knights.

Lantis is a tall, handsome man with short black hair and blue or purple eyes. He is serious, stoic, and a person of few words, often appearing gloomy or expressionless. Despite this reserved exterior, he possesses a very strong heart and deeply cares for those he lets close. He is not sociable or straightforward, but beneath his cold demeanor he is thoughtful and principled. He can be gentle and comforting, particularly toward those who take the time to understand him.

His primary motivation is to destroy the Pillar system, the governing structure of Cephiro that forces a single person to sacrifice their own desires and happiness for the stability of the land. Having witnessed the suffering of his brother and Princess Emeraude under this system, he is determined to prevent such a tragedy from ever recurring. He is willing to fight alone and even give his own life to achieve this goal.

In the story, Lantis initially appears as a mysterious figure whose intentions are unclear. Because of his connection to Autozam and his past as Zagato's brother, many Cephirian magic users distrust him. He nevertheless proves himself a loyal ally to the Magic Knights, joining their efforts to protect Cephiro from the three invading nations: Autozam, Chizeta, and Fahren. His knowledge of both magic and foreign worlds makes him a key strategist and combatant.

His most significant relationships are with Hikaru Shidou, one of the Magic Knights, and Eagle Vision, the leader of the Autozam invasion force. During his travels, Lantis became close friends with Eagle after becoming the only person to defeat him in mecha combat; they respect each other deeply, which creates emotional conflict when they are forced to take opposing sides over the fate of Cephiro. With Hikaru, a bond develops slowly. She is drawn to him out of guilt for having killed his brother, but soon sees past his reserved facade to the loneliness and sadness within. Their mutual affection grows over the course of the second season. In the anime, Lantis eventually confesses his love for Hikaru; in the manga, he asks her to marry him. A fairy named Primera follows Lantis and claims to be in love with him, but he shows no romantic interest in her.

Lantis undergoes notable development from a solitary, mission-driven recluse to a man who opens his heart and learns to trust others, especially Hikaru. His resolve to destroy the Pillar system remains constant, but his methods become less isolated as he accepts help and companionship.

In terms of abilities, Lantis is the only magic swordsman in Cephiro, meaning he is equally proficient in sorcery and swordsmanship. He was Clef's most gifted student in the magical arts, and Clef himself believes his power rivals or even surpasses that of Zagato. His sword is made of light and disappears when not in use. He wields powerful lightning-based magic, such as bolts called Thunders, and can create magical barriers like Cresta. He is also capable of summoning creatures, most notably a flying horse. His physical strength and combat skill are enough to destroy a combat robot with a single sword stroke. The villain Debonair openly covets his power, describing his heart as fearfully strong.