Nebula is introduced as one of the Earth Fairies who was the former Major Fairy of Peace, but now is the Major Fairy of War. She strongly wishes to get her revenge on the Wizards of the Black Circle. In episode 9 of season 4, Nebula possesses Roxy through the White Circle and
goes out to take down the fairy hunters herself with Roxy as her vessel. The Winx Club trail the possessed Roxy to the warehouses on the docks where a battle royale between the Wizards and Roxy ensues. The Winx Club interrupt, much to Nebula's dismay. The wizards escape as the Winx Club are occupying Roxy wondering about her sudden personality change. Nebula threatens to make them pay as they gave the wizards an opportunity to escape by making a large sphere of energy surround her to presumably explode. The Winx Club surround her and make shields that reflect the energy back at Roxy's body, whom suffers the consequences, and not Nebula.
Nebula leads the royal Guard Fairires of Tir nan nog and is the leader of the Warrior earth fairies of Tir NanNog.
Her vendetta against the Wizards of the Black Circle leads her to overthrow Morgana as the Queen of the Fairies with Layla as her second in command. After a heated battle she saw the error in her vengeance and was forgiven by Morgana, the Winx club, and the Fairies of Earth. Nebula then lead the Tir Nan Nor Fairires in restoring the earth with their magic to restore the balance and allow new fairies to be born on earth. Morgana decided to stay with her family and gave the Queen of the Earth Fairires to Nebula who she believed would do an excellent job protecting the earth fairies.
Nebula and Tir Nan Nog fairies restoring earth's winx
Magical Abilities
Nebula casting her spell Electric Storm
Ability-wise, she is extremely powerful as she gave Bloom a run for her money in a one-on-one fight in the episode Bloom's Trial of season four. This most likely makes her as powerful as Icy. Her attack spell Electric Storm seems to indicate some connection to electricity, being that thunder or lightning is a sign of judgement or war. Also she has shown to be very strong in using her Telekinesis in battle and able to shoot very powerful purple, pink, and orange energy beams at her apponent. As the Major Fairy of War Nebula seems to have the empathic ability to manipulate others to her cause to some extent making them wish to fight with her or against her...or it could be her personality.
Nebula using telekinesis
Nebula .vs. Bloom