Helios, who is also known as Pegasus, serves as the holy priest of Elysion and the guardian of the Golden Crystal. In the narrative of the anime, Helios and Pegasus are the same entity, with Pegasus being the form his spirit takes after his physical body is captured.

The character's background is rooted in his sacred duty as the protector of Elysion, the hidden land that safeguards the dreams of the people on Earth, as well as the powerful Golden Crystal. His peaceful existence is shattered when the evil Queen Nehelenia of the Dead Moon Circus attacks him in an attempt to steal the Golden Crystal for herself. To prevent the crystal from falling into her hands, Helios separates his spirit from his captive body and flees, taking on the form of a pure white winged horse with a golden horn, which is the Golden Crystal itself. He seeks refuge within the "beautiful dream" of a pure-hearted individual, which leads him to take up residence inside the dreams of Chibiusa, also known as Sailor Chibi Moon.

In terms of personality, Helios is initially cautious and secretive, as he must protect his true identity and the Golden Crystal from the Dead Moon Circus, which is hunting him by searching the Dream Mirrors of various people. He is portrayed as wise, gentle, and deeply committed to his sacred mission. As he spends more time with Chibiusa, he begins to open up, developing a close bond with her that grows into a deep and affectionate friendship with strong romantic undertones.

Helios's primary motivation throughout the story is to protect the Golden Crystal and the beautiful dreams of humanity from Queen Nehelenia and the Dead Moon Circus. He seeks the one person who can unlock the full power of the Golden Crystal, which he eventually finds in Chibiusa. His role in the story is pivotal, acting as a mentor and power-giver to the Sailor Guardians. He provides Usagi and Chibiusa with the Moon Kaleido Scope and the Crystal Carillon, allowing them to transform into their Super forms. Pegasus can be summoned into battle when Super Sailor Chibi Moon uses the Crystal Carillon to perform Twinkle Yell; he then empowers Super Sailor Moon's attack, Moon Gorgeous Meditation, to destroy the Lemures, the monsters of the Dead Moon Circus.

Key relationships define much of his character arc. His most significant connection is with Chibiusa. He lives within her dreams and relies on her for protection, and their relationship evolves from one of necessity to mutual trust and love, culminating in a kiss and a poignant farewell. He also has a connection as a spiritual guardian to Mamoru, as both are linked to the protection of Earth. Throughout the series, Helios develops from a guarded, secretive figure into a more open and trusting individual who is willing to risk everything for those he loves. His development is also marked by his eventual decision to reveal his true human form and name, Helios, to Chibiusa and the other Sailor Guardians.

Notable abilities possessed by Helios include separating his soul from his body to escape danger and taking the form of Pegasus. In this form, he can fly and enter the dreams of others. He is also able to sense when the world is in danger due to his connection to the Earth. Most importantly, as the guardian of the Golden Crystal, he can lend its immense power to the Sailor Guardians, empowering their transformations and attacks.