Katou mentioned that the previous owner had named it Twilight.
Eterna has a pink hair and purple eyes. She carries a sword on her right arm. Her armor-like clothes are white in color.
In Episode 7, Twilight started taking in Nanase Takeshi's magic power to show him the future by using Nightmare, a magic which can predict an unavoidable future. This had nearly caused him to die, and when he refused to either stay away from Twilight or give it up, Momoka Shijou told him to 'make Twilight his' by defeating it in his dreams. A short battle ensured, with Takeshi losing, and when on the verge of giving up, he realised what Twilight had wanted.
At first Takeshi had no idea she even existed, until she tried consuming all of Takeshi's magic, which would kill him. Takeshi decided to face her and try to make her obey him, but Takeshi was unable to defeat her even with assistance. Before she struck a finishing blow he realized what she want and gave twilight the name "Eterna". Since then there have been no real problems as she now listens to him. After Gekkou took Twilight from Takeshi, she gave him a brief vision of the future and told him to find her. So she now at least prefers Takeshi as her master.
She was one of the legendary 15 magicians from the war 16 years ago and was the original wielder of Twilight.
- The name "Eterna" means Eternally, which means "Being together for Eternity".
- Eterna's clothes resemble Saber's armor in the "Fate/" series
- Her prevous weilder owner named her Twilight because she loved the time when you can see the sun and moon clearly.