Aria Rosenburg (アリア・ローゼンブルグ) is a young girl with long blonde hair and blue eyes. She is the de facto leader of Logos and is the secondary antagonist. Logos believes that she is the sacred maiden blessed by God. She tries to take the Artifacts that seal the Onikirimaru believing that they belong to her.
She is believed to be the incarnation of Monado Cephelot, and is usually referred to as 'the Holy Monado' by Drei. Later on it is revealed that in truth, she bore the same role as the Tamayori Princess and that her mother was murdered by Drei. who's real name is Magus Melchizedek, so that he could raise her in his own interests.
Towards the end of the series, she leaves the Logos mansion with Vier; never to be seen again. She is briefly mentioned that she was grateful to the Tamayori Princess for ending the cycle of torment.
She is quiet and speaks in an adult-like manner but sometimes act like a child. However, she denies so and gets offended when she is called one.
She has a deep attachment to Vier, even going so far as to obey Drei's interests with the knowledge that she was used as a hostage. This might be due to the fact that she doesn't have direct family and Vier was the closest person she had to a family. Likewise, Vier is also fiercely protective of her.
Despite her role as an opponent of the Tamayori Princess and her Guardians, she eventually warms up to them and later on even helps Tamaki by subduing Drei and Zwei; telling the Guardians to rescue her as she and Takuma were about to be sacrificed in an attempt to seal the Onikirimaru.
She is somewhat of a pacifist, as she had spared Tamaki and the Guardians from death during their numerous encounters despite the convenience it would yield in her efforts (much to Drei's dismay).
She is also quite perceptive, as she was able to identify Drei as one of the Four Wisemen due to his overwhelming strength and knowledge.
She can neutralise all magical attacks and bless spirits.