Leon Elliot is a young boy who was born in a country ravaged by a long-running civil war. When he was four years old, soldiers killed his parents. He was subsequently raised and protected by his older sister, but she too was killed when she was caught in a gunfight. These early losses left Leon with a profound distrust of adults and society. As a child survivor of a war that wiped out the adult population, he became wary of anyone older than himself and felt that adults were either indifferent or harmful.

In the anime adaptation of Black Cat, Leon is part of a group of orphans that includes Tim Vertical. The orphans were constantly ignored or abused by the adults around them, which motivated Leon to seek greater power. He wanted to be strong enough to protect his friends. His desire for strength led him to join the Apostles of the Stars, a Taoist revolutionary organization that aimed to remake the world. Ironically, after he gained significant power, he had to leave his friends behind in order to help the Apostles achieve their goals.

Leon has short, bright blue hair and large purple eyes. He often wears a high-collared dark shirt covered by a red jacket. He frequently rides a blue and orange snowboard and sometimes wears goggles. He carries himself with the wary, self-reliant attitude of someone who has learned not to rely on others.

Leon possesses the ability to control air through a Tao power called Wind. He can manipulate air currents to suffocate opponents, create gusts, and perform various aerial maneuvers. This ability gives him a significant advantage in combat, allowing him to attack from a distance and control the battlefield.

In the story, Leon initially appears as a member of the Apostles of the Stars, opposing the main characters. He is eventually defeated by Eve. Later in the narrative, near the final part of the anime, Leon volunteers to retrieve fireworks for Eve. The sound of the fireworks is intended to trigger a reaction that will prevent her from uniting with Eden. During this mission, he becomes exhausted and is about to be defeated by two monsters from Eden, but he is saved by Train Heartnet.

Leon’s key relationship is with his fellow orphans, especially Tim Vertical, whom he tried to protect. His interactions with the main protagonists, Train and Eve, shift from antagonistic to cooperative as he recognizes the need to help stop a greater threat. His development is marked by a movement from self-protective isolation and distrust toward a willingness to assist others, even adults, when the situation demands it.