- Birth Name: Gu Yun (古筠) (Pinyin), Ku Yun (Wade-Giles)
- Stage Name: Xiao Yun (小筠) (Taiwanese), Guu-chan (グーチャン) (Japanese)
- Birthday: December 14, 1996
- Blood type: O
- Hello! Project groups:
- Ice Creamusume (2008–2009)
Gu Yun is the daughter of famous decathlete and pole vaulter Gu Jinshui, and believed she got her hyperactivity and energy from him. Before participating in the Hello! Project Taiwan audition, Guuchan was part of a dance troupe that performed regularly, though due to her activities with Ice Creamusume she did not participate as frequently in their performances. During the audition she was one of the four finalists that made it to the end of the competition.
Due to being busy with school and her dedication to achieving good grades, she did not update her blog frequently while part of the group and was often absent from events and media appearances with Ice Creamusume. In 2009, she graduated from elementary school ranking 10th in her school.
Gu Yun's father was diagnosed with plasma cell lukemia in 2014, and later passed away on May 25, 2016.