Mildred Avallone is a character in the Arcana Heartseries. She started out as the main antagonist of the first game, but after her defeat, she would return in later games as the Arcana of Halo for her older sister, Angelia.
At the beginning of the story, she leads the Norwegian Spirit Society which watches over the Earth from the Arcana realm. They monitor the Maidens - girls gifted with the power of gods and goddesses in the form of Arcana.
Fiona is a maiden who got trapped on the other side and works closely beside Mildred with the two sharing an apparently close bond. Unfortunately, we find that Fiona has tirelessly guarded Mildred without supporting her own well-being. Additionally, Mildred may only have pretended to give affection to Fiona in order to simply take advantage of her vulnerability in loneliness.
In Arcana Heart 2, her very young sister Angelica attains Mildred's power in the form of the Angel Arcana. This is likely her fate for eternity after her failure in the first game.
She is fought at the end of any route in the first game and utilizes all of the Maiden Arcanas in addition to some unblockable angelic attacks.
And she is voiced by Cristina Vee in the English dub and reprised by Yukiko Kikuchi in the Japanese dub.