DANCEROID was formed in 2009 by Ikura, Kozue, and Minka Lee. They started a NicoNicoDouga Community and performed as a trio (and occasionally individual members would upload solo videos) to VOCALOID songs on NicoNicoDouga. They gained popularity so quickly that they released their first DVD [DANCEROID] in December later that year.
After Mikina graduated from the group, Kozue and Ikura preformed as a duo before holding audtions for new memebers that would eventually bring them members: COCO, Maamu, and Yuzuki. However, this group was short lived as COCO graduated, leaving only four girls in the group.
All was well until Kozue found it more and more difficult to preform her duties in the DANCEROID unit. After consulting her doctor, she decided to graduate from the group so she could focus more on her health.
It is unknown to the public exactly what Kozue's health condition is, but she has given us information via her blog. She has posted that she has had poor health since she was a child and had to see many doctors. In a few videos of DANCEROIDing, Kozue has an eyepatch, and in the title of her video "【こずえ】イェイ！イェイ！イェイ！を踊ってみた【あし治りました】" it says that her leg has healed, which we are left to assume was the main reason she left DANCEROID since her eye didn't seem to obscure her work in the unit.