Ero Aoi was born in Sapporo, Hokkaido.

Aoi's musical activities began with participation in a band in high school. Because of her strong desire, she became the lead singer when she was a guitarist. After graduating from high school, she continued her music activities and has been contributing cover works to the Japanese video website Niconico since 2010. He also attracted the attention of composer Fumio Yasuda due to his cover of ピコ's "Story". Subsequently, the fifth CD of the Japanese anime and music magazine ‘Reasana!’ released on April 25, 2011, included “frozen eyez” sung under the name of Eir (Eir). Later, he sang the single "アヴァロン·ブルー" on July 25, 2011.

On August 12, 2011, at the Comic Market 80 held in Odaiba, Tokyo, it made its public debut with the release of the video of the ending theme of "Fate/Zero". On October 19 of the same year, they officially debuted with the release of the single "MEMORIA" which included the ending theme of the film. Both the cover and music video of this single deliberately covered the lower half of his face, and his true appearance was not revealed until the release of his second single "AURORA".

One year after her debut in 2012, she officially announced the release of her first album "BLAU" on her birthday. The singles "Frozen Eyez" and "アヴァロン·ブルー" before her official debut were also included in in this album.

Her alias Eir is mostly used when composing lyrics. I once said that she was deeply influenced by Do As Infinity's Miko Banto, who is also a lyricist.

The characteristic of his singing is explosive high notes.