At a junkyard some secret business seems to be going on when from out of no where Gun’s motorcycle appears. Within a blink of an eye he grabs a briefcase full of money and starts running away. The motorcycle feverishly rides down the road and comes to a stop at an ocean cliff. His motorcycle rides off the cliff and Gun dives right into the ocean. The next day, Gun like any other day goes to the harbor and picks-up the cases of fish to be delivered. Gun gets a phone call from Hyo-joo telling him that someone from the immigration is coming out for inspection. He hurries home where Hyo-joo and Kyeong-taek are busy cleaning up the house.
Dong-ha comes into work, at the aquarium, early and goes around taking a look at every corner of the aquarium. While looking around he sees Ha-neul in one of the tanks surrounded by fish, surprised he jumps in. He is even more surprised when he sees her in a high-school uniform and happens to hear about her from Sun-kyeong. Sung-chan bumps into Ha-neul while trying to get off the bus and pickpockets her wallet. He takes a look inside and is surprised frozen stiff when he sees an old picture.
Gun gets a phone call from Sung-chan telling him that he has found Gun’s little sister. As he hears this Gun’s face grows darker and darker. Hyo-joo asks him what’s wrong but he just acts as if he didn’t hear anything. Also she tells him not to make her worry about him anymore and not to try so hard to make money for her surgery. Hyo-joo goes to sleep and Gun gives Kyeong-taek some information about a hospital. He also gives him some money telling Kyeong-taek that he’s already prepaid. All he needs to do is take Hyo-joo to that hospital and have her go into surgery, and then he leaves to Korea. Ha-neul asks Dong-ha if she can become a diver. He asks her why she wants to become a diver and she answers by telling him it’s because she likes it. Dong-ha starts to think her a bit weird but also shows some interest in her.
Sung-chan sees Gun waiting in front of his house, overjoyed he runs to Gun and greets him. Ha-neul quickly changes into her concert dress and races to the concert hall. Her family awaits her worried but soon as they see her they all get relieved. Gun arrives at the concert hall and tells Sung-chan to wait outside and borrows his clothes. He goes into the concert all and watches Ha-neul from afar. Ha-neul suddenly gets up in the middle of her concert and runs out of the concert hall. She gets into a taxi and is about to leave when suddenly the door opens and Gun hops into the car also.
Ha-neul comes out of her house and Gun follows her. Just then he sees Tae-won’s car and corners her. As she starts to talk he covers her mouth so that she cannot say another word. As Dong-ha leaves the police station he starts to think about what Ha-neul told him. Ha-neul and Gun arrive at the aquarium and enter using the employees’ entrance. The two stand in front of a huge tank and think the same thoughts. Gun is surprised when he hears Ha-neul say that she is going to find her true brother. They are involved in a quarrel about it when Dong-ha walks in.
Sung-chan is surprised when he gets a phone call from Soo-hyun telling him that Ha-neul has disappeared. He sees Ha-neul and Gun going home together and doesn’t know what to do. The next day, Hyo-joo and Kyung-taek come back to Korea from Australia and go straight to Sung-chan’s house. Ha-neul wakes up from her sleep and is surprised when she sees Hyo-joo staring at her. Hyo-joo happily greets by her. Sung-chan doesn’t tell Hyo-joo and Kyung-taek who Ha-neul really is, and Gun, who has come back for the groceries, finds that Ha-neul has disappeared so runs out looking for her.
Sung-chan stops Gun from hitting Tae-won and Ha-neul looks at Gun, surprised by hearing Sung-chan calling him Gun. He angrily takes hold of Ha-neul’s hand and takes her out of the house. Ha-neul asks him if he really is Gun, her brother. Gun gets angry. He yells at her asking her why she didn’t run away from Tae-won earlier. And at this she just hugs him from behind and thanks him for not forgetting about her and coming back to find her. Gun brings Hyo-joo back to Sung-chan’s place. Hyo-joo, Kyung-taek, and Sung-chan all sit down and talk.
Thoughts of Ha-neul keep bothering Dong-ha, and he asks Sun-kyung if Ha-neul still hasn’t shown up for work. Gun goes to the hospital that Soo-hyun is at and politely introduces himself. Ha-neul returns the paycheck that she got earlier than she was supposed to back to Dong-ha, and tells him that she will quit. But Dong-ha asks her if she would like to take a diving course. Hyo-joo comes back from the groceries but ends up overhearing Sung-chan and Kyung-taek’s conversation. From hearing their conversation she finds out that Ha-neul and Gun are not exactly brother and sister.
Gun takes Ha-neul to the house he has bought for the two of them. Surprised, she walks into the house and takes a look around. Gun puts some tropical fish into the fish tank and Ha-neuls starts crying as she sees that Gun hasn’t forgotten the promise they made as a child. Just then Hyo-joo walks in and gives him a kiss and Ha-neul gets surprised. Gun tells Hyo-joo to leave but she tells him that she can’t just leave the two of them together. Gun and Ha-neul cook happily together and Hyo-joo watches them cook then pouts throughout the meal.
The person Jin-kwon sent comes to Sung-chan’s house and he hands him over some money. Kyeong-taek hurries out and jumps in front of the car but Jin-kwon hurries and drives off. Ha-neul wakes up from her nap and runs but suddenly Gun comes next to her, grabs her hand and runs with her. Sun-kyeong tells Ha-neul to go Dong-ha’s house. When she gets there she sees him sleeping and a bottle of sleeping pills lying next to him. As soon as she sees the sleeping pills she is surprised, thinking that he has committed suicide so she slaps him in order to wake him up.
Gun and Ha-neul are surprised when they see Sung-chan and Kyeong-taek waiting for them in front of their house. They hear from them that Hyo-joo has disappeared. Gun gets mad after hearing from Sung-chan what happened, and Ha-neul is curious as to what is going on. Just then Hyo-joo comes in and starts to pack up her stuff. Gun asks her to talk with him first but she tells him that she will leave and promptly walks out. He follows her and is about to tell Hyo-joo that Ha-neul is not really his true related sister, but instead he kisses her, worried that Ha-neul might hear the truth.
Gun and Sung-chan go to Jin-kwon’s office. Gun apologizes to Jin-kwon for their actions and he asks him if he can find them a place to work. Just then Tae-won walks in the door and grabs Gun. Tae-won asks Gun where Hae-won is but Gun tells him to erase that name from his head and leaves. Dong-ha tells Ha-neul that all the employees are going out to dinner together. Ha-neul tells Gun that she will also try to make some money for Hyo-joo’s surgery, but Gun just gets angry at her. Dong-ha tries to take Ha-neul, who has become drunk from the dinner, home, but she tries to call Gun instead.
When Gun sees Tae-won, he drags him out and throws a punch at him. They eventually get into a fight and Gun is about to throw the last punch at Tae-won when he quits, turns around and leaves. Tae-won gathers himself up; when he sees a broken champagne bottle he picks it up and stabs Gun with it. Dong-ha changes into Gun’s clothes and sits awkwardly and Ha-neul hands him a handkerchief. Hyo-joo suddenly asks the two what relation they are. Dong-ha tells her that they are lovers and at hearing this Ha-neul is completely surprised. Ha-neul is scared to death when she sees Gun come home covered in blood and faints in her arms.
Everyone hearts are soothed when they hear that Gun is not in critical condition and Ha-neul goes out to find Tae-won. She finds him and grabs him, telling him that if he ever lays his hands on Gun again she’s not going to leave him alone. As she turns to leave Tae-won goes after her and tells her that the only reason why Gun came back was to get some money from her. Gun wakes up and looks for Ha-neul; just then she walks into the hospital ward. As she sees that he is okay she starts crying in his arms. Gun gives his shark tooth necklace, the one he always wears, to her as a birthday gift.
Ha-neul goes to Sung-chan’s house and overhears a conversation between Gun and Hyo-joo. From their conversation she finds out that Gun is not her full brother. Gun and Hyo-joo glare at each other and Gun leaves the room. Ha-neul, surprised at finding out the truth, hides in a corner in the rain and watches Gun as he walks by. Dong-ha sees Ha-neul standing in front of the main tank. Drenched in rain she starts to cry her heart out. Dong-ha takes her home and offers to be her life insurance if she’d like, but she just smiles. Ha-neul asks Gun to make her some ramyun. At his warmth tears start to come to her eye and in order to hide them she starts being fretful towards him.
Even though Ha-neul feels sick she still goes into the fish tank. Gun, worried about Ha-neul because she didn’t have any breakfast, goes to the aquarium with Sung-chan to see her, but Ha-neul faints inside the tank while doing a show. Gun, watching all this, becomes surprised and dives into the tank in order to save her. Ha-neul lies on her bed and Gun looks at her with worried eyes. Dong-ha comes to the house to check up on Ha-neul but Gun throws him out. Ha-neul wakes up and apologizes to Gun for her actions; also she asks him why he came back to her.
Ha-neul goes to Dong-ha’s office and as soon as Dong-ha sees her he is relieved, but at the same time gets angry at her. She apologizes to him but he tells her to go out. Then he goes up behind her and hugs her thanking her for coming back safe and sound. Ha-neul calls Gun to tell him that she thinks she is going to be a little late and asks him if he can come to the aquarium. Hyo-joo gets a text message from Gun and goes to the aquarium. Hyo-joo finds Gun and runs to him and hugs him. Surprised, Gun just stands motionless. Ha-neul and Dong-ha watch the two from afar and Ha-neul, feeing somewhat bitter, thanks Dong-ha.
Gun gets home and asks Ha-neul why she did such a thing when he didn’t even ask for it. Ha-neul takes the necklace Gun gave her off her neck and gives it back to Gun telling him to give it to Hyo-joo. She tells Gun that she thinks it might by better if he went back to Australia and he just looks at her with a stern look. Dong-ha uses the coupon Hyo-joo gave to him as an excuse and asks Ha-neul to have dinner with him. Just then Gun comes to the restaurant Hyo-joo works at and sees Ha-neul and Dong-ha together. Ha-neul gets a phone call telling her that Tae-won has taken some pills and is in the hospital. She goes with Gun to the hospital.
Ha-neul asks Dong-ha to wait for her, then goes home and starts packing her stuff. Hyo-joo tries to stop her but Ha-neul does not listen to her. Gun later comes out and grabs her arm but she gives him the cold shoulder and tells him that she doesn’t understand why he’s doing this when he isn’t even her real brother. Gun is surprised to know that Ha-neul knows the truth and asks her to go inside so that they can talk, but she gets into Dong-ha’s car and leaves. Dong-ha takes her to his house and tells her that she can stay there for a while and that he will go someplace else. Dong-ha cooks some noodles for her but tears start to come to her eyes because it reminds her of Gun.
Gun waits in front of the aquarium all night for Ha-neul. As he sees her come into work in the morning he tells her that it was not all because of money that he came back for her; it is was because he really wanted to see her. She works hard to ignore him. Gun and Sung-chan go to Jin-kwon’s company. When Gun sees that he has moved into a new office and his title has become the executive managing director he calmly gives the secretary some instructions. Ha-neul tells Dong-ha that she is moving into her mother’s house, but goes to a hotel and tries to sleep there. Because of Sung-chan’s request Mal-ja asks Ha-neul if she would like to go out for dinner with her. So Ha-neul goes to dinner with Mal-ja and Dong-ha, and there she runs into Gun.
Hyo-joo secretly follows Ha-neul, who has just gotten off work. Ha-neul, feeling a strange feeling, looks back and sees Hyo-joo, but acts as if she didn’t see her and keeps on walking. The two sit down inside Ha-neul’s hotel room and Hyo-joo tells her that everything Gun did was because of her and that nothing is his fault. Gun watches Ha-neul going into a hotel and is devastated. He asks Dong-ha to persuade her into coming back home again. Dong-ha dresses Ha-neul up in some nice clothes and takes her to the beach. Dong-ha tells her that today is the day her and Gun’s parents passed away and he tells her to go to him. Gun apologizes to her and asks her to come back to the house.
Ha-neul walks back home from the grocery store and is surprised to see Tae-won waiting for her. She tell him that she does not want to go anywhere with him, but he forces her into his car and drives away. Gun, on the way home, sees Ha-neul so he turns his car around and starts following Tae-won’s car. After a lengthy pursuit, Tae-won runs into the railing on the roadside, which finally brings the car to a stop. Gun helps Ha-neul get out of the car and asks her if she is OK. Gun and Ha-neul drive back home but on the way Gun starts to feel confused, thinking about the past. Ha-neul looks at Gun with a very worried look. Suddenly he stops the car and in shock looks at Ha-neul. She asks him what’s wrong but he just hugs her.
Ha-neul goes out to drink with Mal-ja and gets drunk, so Mal-ja calls Dong-ha. But Ha-neul calls Gun and says ‘Superman returns.’ As Gun hears this he quickly gets into his car and starts driving. Gun helps Ha-neul up and tries to take her to the car but she stumbles and ends up in Gun’s arms. Gun is startled when Ha-neul asks him why his heart is beating so fast. Dong-ha arrives a few minutes later and just watches the two. Dong-ha walks up to Gun and takes Ha-neul out of his arms telling Gun that this is something a boyfriend should do. Then he picks her up and takes her to his car.
Dong-ha gives Ha-neul some papers that she needs to get into school and tells her that if she is in any trouble to call him. Dong-ha is imagining Ha-neul kissing him, when he is awakened by Sun-kyung’s voice. As he opens his eyes he surprised to see her right under his nose. Hyo-joo starts crying when Gun tells her that there has never been a single moment he’s loved her. As she starts crying he hugs her and starts to comfort her. Ha-neul and Dong-ha go to the hospital to see how Hyo-joo is doing and end up seeing the two together. As Ha-neul sees the two hugging each other her face stiffens. The four sit in the hospital ward and a strange atmosphere starts to form. Gun tells Ha-neul to leave, so she starts to feel bad and looks back at Gun.
Gun has a hard time believing that Ha-neul is Tae-won’s real little sister. Shocked, he drives full of anger and sadness. Ha-neul starts to worry as Dong-ha, without a word, doesn’t show up at work, so she goes to look for him. Dong-ha sits by a lakeside, looking lonely, fishing. He is surprised when he sees Ha-neul. She tells him that she has decided to follow him. As Ha-neul turns around to leave he turns her back around and kisses her. Gun comes home after drinking, and when he sees Ha-neul waiting for him his heart breaks. He hugs her and tears fall from his eyes.
Gun gets into a fight with another customer at a little outdoor bar and gets driven to the police station. As soon as Ha-neul gets a phone call telling her that Gun is at the police station she runs straight to him. Ha-neul tries to treat his wounds but he pushes her away and leaves the room. Ha-neul looks at Gun, who has fallen asleep on the couch, with a worried look. While she disinfects and treats his wounds tears start to fall from his eyes. Ha-neul gets shocked when Hyo-joo tells her that Gun thinks that Jin-kwon killed their parents. Ha-neul sends a text messages to Gun telling him that she will be waiting for him at a pedestrian overpass, so Gun goes to see her.
Gun and Ha-neul leave together on a little trip, and Ha-neul’s phone rings but she doesn’t answer it. They arrive at a little village next to the ocean where they scream and play in the ocean like little children and spend a wonderful time together. The two go to a marketplace and all around the town. They end up holding each other’s hand and act as if nothing has happened, but their minds are all on their hands. Ha-neul is in the room when she hears raindrops falling. Worried about Gun, who is outside, she gets up. Gun comes into the room and lies down away from Ha-neul then falls asleep. Gun wakes up in the morning surprised to see Ha-neul sleeping in his arms. But he just stays still and gazes at her sleeping.
Ha-neul comes back to Seoul and apologizes to Dong-ha, and he asks her where she was. At this she just asks him to not to ask her any more questions. Gun goes to Jin-kwon and tells him that he will let everything pass by and continue as if nothing happened and that they must make sure that Ha-neul never ever finds out about the truth. Ha-neul goes out to have dinner with Dong-ha but is surprised to find Gun there. Gun gets angry at some of Dong-ha’s words and leaves, and Ha-neul tells Dong-ha that she is not going to go to America with him. Dong-ha asks Gun if he really thinks of Ha-neul as his little sister. As Gun hears this he punches Dong-ha. Gun spills out his heart to Dong-ha and tells him that he loves Ha-neul, but he has to let her go and then leaves.
Gun tells Ha-neul that he will take care of everything and that she should pretend not to know anything. Gun tells his lawyer to place all the assets that were handed over to him back to the way they were. Hyo-joo starts to cry but holds in her tears as Gun gives her an account booklet and plane ticket. Dong-ha’s heart breaks as he looks at the ring case and letter of resignation on his desk. He asks Ha-neul what he was to her and after she leaves his office he tries to act as if he is alright, but tears fall from his eyes.
Tae-won tells Ha-neul that Jin-kwon is her real father. She becomes shocked and goes straight to Jin-kwon. Ha-neul calls Gun out to a bus stop, goes out to see her and sits next to her. Ha-neul tells him that she is about to give him a prize and holds his face with her hands. She thanks him for loving her and kisses him. Kyeong-taek and Sung-chan find Hyo-joo fainted on the floor of their house and take her to the emergency room. Kyeong-taek spits out some venomous words to her, and Ha-neul just sits and listens with tears rolling from her eyes.
Ha-neul and Gun are driving back home when Gun’s phone rings. He gets a phone call from Tae-won telling him that Jin-kwon has passed away. They arrive at the funeral home and Ha-neul tells Gun that it would be better if she goes in alone. Gun gets another phone call telling him that Hyo-joo is in critical condition, so he goes to the hospital she’s at. Tae-won asks Ha-neul how she can act so coldly in regards to her father’s death. Ha-neul wanders away and starts crying, with Dong-ha following her and watching her with a broken heart. As she stops crying he walks up to her and tries to comfort her. Dong-ha tells Gun to stop making Ha-neul so confused and take good care of her.
Hyo-joo asks to get discharged from the hospital and asks Gun if he will come to Australia with her and Gun has trouble refusing her request. Dong-ha tells Ha-neul that he would like it if she kept on working at the aquarium and that he is going to leave as planned. Gun and Ha-neul go to an amusement park and spend the day together. Gun hugs her and tells her that he is going to go away for just a little while. At this Ha-neul tells him not to take too long and that she’ll be waiting for him, so to be sure to come back for her. Three years have passed and on the way to work Ha-neul runs into Dong-ha. Gun comes back and goes to all the places he and Ha-neul went to together, then heads towards the aquarium.