BY2 consists of Singaporean twin sisters Miko (孫涵) and Yumi Bai (孫雨) who were born in Yio Chu Kang, Singapore on March 23, 1992— Miko is the eldest of the two while Yumi is the youngest. They are among the most internationally recognized Singaporean acts alongside the likes of JJ Lin and Stefanie Sun.
The twins had a passion for dance and music at a very young age, as they learned violin, piano, ballet, and many other styles of dancing such as Chinese traditional folk and ballet. As they grew older, they learned more modern forms of dance such as hip hop and street dance; their father was a driving force in nurturing the twins' career in music. However, he would pass away in 2007 before witnessing his daughters' debut and rise to stardom.
In 2007, they moved to Taiwan and joined Ocean Butterflies' Music Forest’s V Singer (“非常歌手”) training course at the age of 13 where they graduated with a “Best Costume Design” award and were granted a 10-year contract after being noticed by Billy Koh of Ocean Butterflies Music. Miko and Yumi were later sent to various countries in order to train and hone in their vocals and dancing skills.