It is magically opposed to the White Circle, and was created by the Wizards when they started the Great Fairy Hunt to combat the powers of the White Circle. Its powers are to seek out, capture, and imprison Earth Fairies as well as to steal their magic powers by plucking their wings. The Black Circle is the magical opposite of the White Circle.
According to Ogron, it is the source of the power of the Wizards. However, after the Black Circle is destroyed when Morgana is tricked into wearing it, the Wizards still have their powers, though this could be because the Wizards already had magical powers before creating the Black Circle.
When the Wizards captured Earth Fairies and plucked their wings, they also stole their power which was absorbed into the Black Circle. The Wizards of the Black Circle then imprisoned the Earth Fairies themselves in the realm of Tir Nan Og. It is assumed the the Black Circle had fed upon the agony and the power of the Earth Fairies in their imprisonment. When the Winx freed the Earth Fairies, the Wizards were greatly weakened as the energy that had been absorbed in the Black Circle was now free and the Black Circle could no longer feed upon the captured Fairies' power.
It was first seen in "A Virtual World" when the Winx used their Tracix wings on the White Circle to look into its past. There, they learned that the White Circle is the Earth Fairies only hope to combat the Black Circle.
Then, in "Sibylla's Cave", when the Wizards began to weaken due to the growing belief in magic, they appeared before the Winx asking for their assistance. Ogron decided to surrender the Black Circle, where all of the Wizards' powers are contained. Anagan proposes to give the Circle to Morgana as a sign of surrender. Bloom takes it and shrinks to a ring size and keeps it in her presence. The Winx decide to help them and chose Sibylla's cave as their safe haven. Sibylla is the most pragmatic choice, for as the Fairy of Justice she must remain impartial to all and will therefore protect all who come to her. Also, her caves prohibit Earth Fairies to enter, making it the perfect place for the Wizards to seek refuge.
In "The Day of Justice", the Wizards are brought to Tir Nan Og to await their judgement. The Black Circle is placed within a chest for safekeeping until the Wizards are brought to trial. It is revealed by Duman, who has gone mad due to his unstable magical energy, that when Morgana places the Black Circle on her finger, all Earth Fairies will be destroyed.
When the Ceremony of Truth begins, Morgana places the Circle on her finger, activating a dark abyss that attempts to suck all Earth Fairies into it. However, this is prevented at a great cost as Nabu sacrifices all his energy to close the abyss, saving the Earth Fairies. He perishes in Aisha's arms.
- It is unknown if the Black Circle is truly the source of the Fairy Hunters' magic, considering Ogron had lied about their situation in order to try destroy the Earth Fairies.