Yoon Sefan is a fairly good natured girl with a usually cheery disposition. However she is clumsy, somewhat flight, and is easily brought to tears in a "crybaby" fashion. This combination makes her seem childlike, though she has a serious love for engineering and technology.
Yoon Sefan is a young female Orb civilian who originally worked as an Engineer for Morgenroete Inc, however she got left behind during the evacuation in the year C.E 71. Thankfully she managed to avoid capture by the Earth Alliance and found sanctuary with the Junk Guild. She would continue to work as an engineer, proving invaluable by creating the MWF-JG71 Raysta, a Junk Guild exclusive mobile suit based on Orb's MBF-M1 Astray. At one point in C.E. 72 she was in South America performing a job. When she finished and was on her way back she accidentally came across a battlefield where Earth Alliance mobile suits destroyed by a single ZAFT machine, the ZGMF-X999A ZAKU Trial Type. Its pilot, Courtney Heironimus attempted to kill Yoon to keep the information secret, however she was saved thanks to "God Fist" Barry Ho.