Soo Ae
"Sunny" was produced on a budget of (). Director Lee Joon-ik made the protagonist female in response to criticism that his films were largely male-oriented. Lee cast Soo Ae in the lead role, saying, "No other actress in [South] Korea has the distinctively pure image that [she] has". Soo Ae did two months of training to refine her singing and dancing skills, and admitted to being concerned over whether or not she could pull off the character.