200 Pounds Beauty (2006) on Netflix

Plot summary

Hanna Kang, overweight and mocked for her looks, works as a ghost singer, supplying the vocals that the popular singer Ammy lip syncs on stage. Hanna nurses a crush on Sang-jun, a director at the label his father Choi owns. When Ammy sets out to humiliate her at Sang-jun's birthday party, Hanna overhears Sang-jun urging Ammy to keep her close so her voice stays available. Heartbroken, she agrees to let Kong-hak Lee, a plastic surgeon who calls her phone line, remake her from head to toe. A year later she is slender and unrecognizable, and with help from her friend Jung-min Park she returns as Jenny, a Korean-American from California.