Eun-ha is the dead fiancée of a rich heir, while Ji-sook is a doppelganger forced by his rival to assume her identity and proceed with the marriage of convenience.
Eun-ha (in writing) and Ji-sook (in person): One who dons a mask will ultimately be unhappy.
Ji-sook (continuing): One cannot be happy living with someone she does not love while pretending to love him from behind a mask. Hence, I will live my life loving him—for real.
Walt Disney director and writer Jennifer Lee, whose credits include award-winning animated features Frozen and Wreck-It Ralph, said that the first thing students learn in film school is character. The worst characters are thought to be perfect characters, who feel inauthentic. Characters second only to them are those full of self-doubt. The central character of Mask, unfortunately, was one or the other most of the time. She started off as a clumsy doormat wearing her heart on her sleeve while everyone else was donning masks, even though she was supposed to be the one hiding her identity. In the second half of the series, she veered to the opposite end, playing a confident and impeccable Santa Claus to all except her nemeses. For a brief, golden period in-between, though, Ji-sook was a woman who roused roaring support from the audience as she finally studied the mindset of her tough doppelganger and stood up to her tormentors, having come to the realization that she could defend those she loved only by becoming stronger, or in other words, becoming her mask.