In the anime Sailor Moon SuperS, the character known as Pegasus is the visible form of a young man named Helios, who serves as the holy priest of Elysion. Elysion is a sacred, hidden land that exists within the Earth and is intrinsically connected to the planet's dreams and the legacy of the Golden Kingdom. Helios's primary duty is to act as the guardian of the Golden Crystal, a powerful artifact that sustains and is sustained by the beautiful dreams of all people on Earth. The golden horn on Pegasus's forehead is this very crystal.

The story of Helios begins with a threat to his domain. Queen Nehelenia, the ruler of the Dead Moon Circus, seeks the Golden Crystal for herself and attacks Elysion. To protect the crystal and find a way to fight back, Helios is forced to separate his spirit from his physical body, which is captured and held prisoner by the queen. His disembodied spirit, seeking a place of safety and purity, transforms into the form of a winged white horse, a Pegasus, and seeks refuge within the beautiful and untainted dreams of a young girl, Chibiusa, also known as Sailor Chibi Moon. It is almost exclusively in this equine form that he interacts with the world throughout the series.

In terms of personality, Helios is defined by his deep sense of responsibility, his initial reserve, and his unwavering commitment to his mission. As the guardian of dreams and the Golden Crystal, he carries a heavy burden and is cautious about revealing his true nature or the details of his predicament. When he first appears to Chibiusa as Pegasus, he is secretive and speaks in riddles, driven by the singular goal of finding a "maiden with a pure heart" who can unlock the full power of the Golden Crystal. He is kind and gentle, particularly towards children and their dreams, but his fear of Nehelenia finding him makes him wary. However, as he spends more time in Chibiusa's dreams and witnesses her courage and pure heart, he begins to trust her, and his more vulnerable and sincere personality emerges.

The central relationship in SuperS is between Helios in his Pegasus form and Chibiusa. He chooses her dreams as his sanctuary because they are the most beautiful and innocent he can find. She is initially the only one who can see, hear, and summon him. Their bond grows from one of necessity to a deep, emotional connection. Helios equips Chibiusa with a special bell called the Crystal Carillon, which she uses to perform "Twinkle Yell," summoning him to the physical world. Once summoned, Pegasus lends his power to Chibiusa and her mother, Sailor Moon, allowing them to transform into their Super forms and use powerful attacks like Moon Gorgeous Meditation to defeat the Lemures, the monsters of the Dead Moon Circus. He also gives the other Sailor Guardians their Crystal Change Rods, enabling them to power up as well. As the series progresses, Helios eventually reveals his human name and form, sharing a kiss with Chibiusa as their mutual affection becomes apparent. He is also connected to Mamoru (Tuxedo Mask), who is the modern-day counterpart of Prince Endymion; as the priest of Elysion, Helios is the guardian priest to Endymion, making their fates intertwined.

Helios undergoes significant development through his relationship with Chibiusa. He begins as a distant, mystical figure who is purely goal-oriented, seeking a tool to defeat his enemy. Through Chibiusa's unwavering belief in him and her refusal to give up, he learns to trust again and rediscovers the power of personal connection. His motivations shift from simply surviving and finding a wielder for the crystal to a desire to protect the people who have become dear to him, particularly Chibiusa. By the end of the arc, after he is freed from Nehelenia's curse, he is shown to be a more open and hopeful person, looking forward to the future and to seeing Chibiusa again.

Helios possesses a range of notable abilities tied to dreams and his role as a priest. His primary power is dream manipulation, allowing him to enter, reside within, and communicate through the dreams of others. He can separate his soul from his physical body, taking the form of Pegasus. In this form, he can fly and become visible in the real world when summoned. His most crucial power is the ability to lend his own magical energy and the power of the Golden Crystal to other warriors, amplifying their attacks. He also possesses extrasensory abilities, allowing him to sense danger to the Earth and to locate individuals with pure hearts. While his physical form is held captive, he demonstrates incredible resilience, enduring torture to protect his allies and the crystal. The Golden Crystal itself, sealed within his forehead, is the ultimate source of his power and the primary object of Nehelenia's desire.