She is an elementary Year 5 student. She tried to disguise herself as Tomoko Saitou (サイトウトモコ Saitō Tomoko?), Haruyuki's second cousin, in order to cage him inside his house but failed.
Yuniko was abandoned by her parents and attends a school for abandoned children.
Mentally, she's older due to spending a lot of time in Accel World.