Sun-Hwa Kwon (Yunjin Kim) on "Lost" was born into the powerful Paik family, owners of Paik Automotive. She was to have an arranged marriage to Jae Lee (Tony Lee) but discovered he was in love with an American woman and married Jin-Soo Kwon (Daniel Dae Kim) instead. Sun and Jin soon experienced marital problems that worsened after they learned that Sun was infertile. Sun planned to escape her marriage in Australia by using a false identity but hesitated and boarded Oceanic Flight 815 with her husband.
After crashing on the island, Sun is domineered by Jin's personality. She also conceals the fact she knows English from everyone, including her husband. During their experiences on the island, they began to rebuild their relationship with Jin vowing to be a better and more loving husband. Sun discovers that she is pregnant and tells Jin that he is the one who is infertile not her. She does not tell him about her affair with Jae Lee.
Sun finds out from an "Other", Juliet Burke (Elizabeth Mitchell) that pregnant women die on the island. They search for fetal monitoring equipment and discover that Sun conceived on the island, thus making Jin the father. She also learns that she only has two months to live.
Sun is one of the first people to leave the island for the freighter where she sees Michael (Harold Perrineau) and discovers that the freighter is wired with C4. She is able to escape on a raft but watches in horror as the freighter explodes with Jin on it. The raft drifts aimlessly until it bumps into Penelope Widmore's (Sonya Walger) rescue ship.
Sun goes home and is known as one of the "Oceanic Six". The group makes up cover stories to protect the island and the survivors they left behind. In her cover story Jin died in the crash. It is not exactly determined if she was compensated from the airline, or if she had some unknown source of money, but she buys the majority share of her father's company. Sun gives birth to a healthy baby girl several months later and names her daughter Ji Yeon honoring Jin's wishes.
Sun is given proof that Jin is still alive and well on the island and boards another flight to find the island. This plane crashes as well and Sun finds herself back on the island where she meets John Locke (Terry O' Quinn) who promises to reunite her with her husband. Sun finds out that Locke is an imposter. This is proven when she sees Locke's dead body in a coffin, dumped on the beach.
The Man In Black tries to talk Sun into following him by claiming that he has Jin. She runs off knocking herself unconscious. When she awakes she can no longer speak English, only write it. Upon heading for the docks she runs into Jin. Sun is able again to speak English just in time to be thrown into a cage. She and Jin escape to the submarine where inside they discover C4. The C4 detonates pinning Sun under debris. She begs Jin to leave, but he ignores her pleas and they die together hand in hand.
"Being told what to do was my life for four years... I didn't like it much either."
"You don't know what my husband is capable of."