A Daring Deception(2003)

Hanayaka na Adventure

The blue eyes that attract any woman... His deep gaze... Rachel cannot stop her heart from pounding when she sees her beloved Nathan, a breathtakingly gorgeous man from her work. But for some reason he thinks she is a cunning and promiscuous woman and always gives her the cold shoulder. One day, Rachel's grandmother makes a shocking request, and Rachel ends up going on a trip alone with Nathan. Her job is to act as Nathan's girlfriend and get back her grandmother's stolen letters.

(Source: Renta!)