In Sailor Moon SuperS, Helios is the high priest of Elysion, a hidden realm connected to the Earth Kingdom, and the guardian of dreams. In the anime, the winged white unicorn known as Pegasus is his alter ego, the form his spirit takes after Queen Nehellenia captures and imprisons his true body. While Nehellenia seeks the Golden Crystal he protects, Helios escapes as Pegasus and takes refuge in the pure, beautiful dreams of Chibiusa, where he can survive.

As a character, Helios is gentle, calm, and deeply compassionate. He carries a quiet sense of duty and self-sacrifice, placing the protection of Elysion, the Golden Crystal, and the dream world above his own freedom. He is also somewhat reserved and secretive at first, deliberately keeping his true identity and circumstances hidden from Chibiusa because revealing them could endanger her and the other Sailor Guardians. Despite this guardedness, he genuinely cares for others and offers patient guidance and reassurance, especially to Chibiusa.

His central motivation is to protect the Golden Crystal from Nehellenia and restore Elysion to its former state. He also wishes to safeguard the dreams of innocents, which Nehellenia and her Dead Moon Circus threaten to consume. Because he cannot survive long outside of a pure dream, he depends on Chibiusa's kindness and eventually comes to trust her completely.

In the story, Pegasus serves as a guide and ally to the Sailor Guardians. He appears to Chibiusa in her dreams and, when summoned, grants Sailor Moon and Sailor Chibi Moon enhanced power, transforming them into their more powerful Super forms. He provides them with new tools, including the Crisis Moon Compact and the Chibi Moon Compact for their transformation, as well as the Kaleido Moon Scope for Sailor Moon and the Crystal Carillon for Sailor Chibi Moon. Through these gifts, the Sailor Guardians are able to fight the Dead Moon Circus and defeat the Lemures creatures. Later, he also empowers the Inner Sailor Guardians, granting them their own Super forms.

His relationship with Chibiusa is the emotional core of his role. At first, he keeps many secrets from her, but over time the two form a close and affectionate bond. He offers her advice about friendship, love, and growing up, and she comes to trust him deeply. Their connection grows into something romantic, culminating in a shared kiss within the dream world. When Nehellenia finally discovers Pegasus hiding in Chibiusa's dreams and places her under an eternal sleep, Helios is moved to reveal his true human form and identity to the Sailor Guardians so they can rescue her.

Throughout the season, Helios develops from a mysterious and cautious presence into a devoted protector who is willing to reveal himself and risk everything for the people he cares about. After the Dead Moon is defeated, he takes the Golden Crystal back to Elysion, leaving Chibiusa with the promise that their paths will cross again in the future.

Notable abilities include appearing and communicating within dreams, telepathic speech, transforming between his Pegasus form and his human form, and channeling the power of the Golden Crystal, which is represented by the horn on Pegasus's head. This crystal is central to the defeat of Nehellenia, as its power allows the Sailor Guardians to combine the dreams of others and seal the queen away. In the anime, Helios is considerably more powerful than in the original manga, capable of granting permanent upgrades to the Sailor Guardians, summoning magical weapons, and lending his energy to their strongest attacks.