Eir Aoi is a singer-songwriter. After releasing videos on Niconico, she made her major debut with SME Records in 2011. She released 13 singles, 4 albums, and 2 greatest hits albums with the label.

After concluding a two-night farewell concert at Nippon Budokan, she went on hiatus in November 2016 due to health issues. In February 2018, it was revealed that she had signed with SACRA RECORDS to release her 14th single. At the end of December 2023, she announced the end of her contract with SACRA MUSIC.

She credits herself as simply "Eir" for compositions and lyrics. Her real name is Yui Aoyama (青山由依).