Erin Suda (エリーヌ 須田, Erīnu Suda) is a third-year transfer student to AGHS from the United States. She is also the Aquarius Zodiarts (アクエリアス・ゾディアーツ, Akueriasu Zodiātsu), a member of the Horoscopes who evolved from an unspecified Zodiarts. She was discovered by the Libra Zodiarts using his Eye of Laplace.

Erin transferred to AGHS from an American school to pursue her dream of becoming an astronaut. She aims to be the first person in her family to go into space. Her passion for space is inspired by her father, an astronaut who, despite his talent, never made it into space, as he was passed over for someone with less skill but more charisma.

Erin eventually takes up the Aquarius Switch, believing that the advantages of a Zodiarts body will aid her future space career. Despite this, she remains determined to become an astronaut based on her own abilities.

Erin is somewhat easily excitable, as seen in her love for space. She also goes out of her way to made it clear she wants to get the best scores on the astronaut exams. She is also cold and calculating, and takes the exams very seriously. When angered she quickly loses her cool, becoming enraged and even vengeful, though such instability, a well-known side-effect of the Switch use, is likely due to her Zodiarts status.