Aria, whose full name is Aria Rozenburg, is a primary antagonist in Hiiro no Kakera - The Tamayori Princess Saga. She is the leader of an opposing faction known as Logos, which she sometimes refers to by the same name. Aria is depicted as a young girl, and she commands her own group of followers who are loyal to her cause.

In the story, Aria and her organization are directly opposed to the Tamayori Princess and her guardians. Their central goal is to challenge the princess's mission of protecting the sacred sword Onikirimaru and the seals that keep a world-ending demon imprisoned. Aria is a formidable enemy, and her forces are shown to be powerful enough to defeat the princess’s guardians in battle. During one major confrontation, she and Logos overwhelm the guardians, forcing the protagonist Tamaki to bargain for their lives by handing over one of the crucial artifacts she is meant to protect. Aria arrives in the town where the story takes place to investigate disturbances related to the Tamayori Princess and the seals, accompanied by her assistant and interpreter, Yorihisa. Her presence creates a direct and persistent threat, and she questions the princess and her guardians about their actions.

Aria has connections to other characters that add complexity to the conflict. One of the princess’s own guardians, Shinji Inukai, shares a dark history with her organization. The nature of this past is so significant that Shinji eventually leaves the guardians to meet with Aria and discuss it, though he is ultimately rejected by her and cast out. Another guardian, Suguru Oomi, defects to join Logos, rising to a high rank within her group. These defections highlight Aria's influence and the internal strife she causes among the protagonists.

Specific details about Aria's background, personal motivations, supernatural abilities, and character development over the course of the series are not available in the search results.