Father to Sun and Joong-ki as well as a powerful businessman based in Seoul.
- HeelFace Door-Slam: Just as he decides to come clean about the embezzlement and get his daughter out of prison, Joong-ki murders him.
- My God, What Have I Done?: He comes to this realization after convincing Sun to go to prison for his and Joong-ki's sake. When he visits her, he admits he hasn't been taking care of himself at all out of shock.
- Parental Favoritism: He pretty clearly favors his son over his daughter, which his children are very aware of. In fact, he acknowledges his daughter so little that this is basically the entire reason the plan for Sun to take the fall for the embezzlement works - despite being his child and employee, there's almost no public connection between them.
Sun's younger brother who also shares a high position in their father's company.
- Ain't Too Proud to Beg: Begs Sun not only to take the fall in the first season, but also when she's about to kill him with a piece of rebar.
- Cain and Abel: He eventually tries to have Sun bumped off, because She Knows Too Much.
- Corrupt Corporate Executive: His embezzlement is what gets the company into trouble in the first place.
- Crocodile Tears: When he tells Sun that their father killed himself and she promptly replies by accusing Joong-Ki of murdering him, all pretense of grief immediately fades.
- Dirty Coward: Will do anything he can so that he wouldn't have to face the music.
- Establishing Character Moment: His first appearance is him arriving late to a meeting with a client, whom his sister has to deal with as a result; he also cheerfully ignores the sexist way the client treats Sun.
- The Evil Prince: Though not royalty, he fits the archetype, being a petty, spoiled, greedy man born into a rich and powerful family, who then goes on to kill his own father and then trying to usurp and get rid of his much more morally upright and responsible older sibling.
- Foolish Sibling, Responsible Sibling: Joong-ki is a freeloader who causes all of his family's problems, which Sun has to clean up by going to prison for his embezzlement.
- Hate Sink: There is nothing likable about Joong-ki; from his first appearance he establishes himself as selfish, hedonistic, and uncaring about his family, and it only gets worse from there.
- Hookers and Blow: The second time we see Joong-ki is at a sex club where he and his friends are pawing at the performers and getting drunk.
- Jerkass: Constantly insults and dismisses Sun, and has no qualms about transparently trying to manipulate her into going to jail for him.
- Karma Houdini:
- Karma Houdini Warranty: In the Series Finale, the politician who had his back is investigated for corruption, ultimately bringing down Joong-ki with him.
- Make It Look Like an Accident: Sun suspects that he murdered their father to spare his own reputation. His reaction suggests she's right.
- Spoiled Brat: Joong-ki has clearly developed no accountability as a result of his father's favoritism, blaming his father for his embezzling of millions from the family company because their father "taught [him] how to bend the rules".
- Villain with Good Publicity: Sun takes the blame for his embezzling and no one suspects him of killing his father. As of the Christmas special, he gets both praise for "saving" the company and sympathy for having an "unstable" sister. When Sun tries but fails to kill him in season 2 second last episode, he gets even more sympathy and she's labelled a dangerous fugitive. In the Series Finale though, the public finally get wise to his ruse when the corrupt politician protecting him is brought down by the police.
Sun and Joong-ki's deceased mother.
- Deceased Parents Are the Best: She was kind, gracious, and supportive of Sun, in stark contrast to Sun's father.
- Deliberate Values Dissonance: While close familial ties are valued across all cultures, the promise Sun made to her to always look after her brother and father is very clearly based on a more East Asian view.
- Missing Mom: She died of illness (implied to be cancer) when Sun was a child.
- Parental Favoritism: She was closer to Sun than to Joong-ki as a result of her husband preferring him.
One of Sun's fellow inmates.
- The Dog Bites Back: Decided to poison her husband when she had enough of his abusive behavior. She spots the same attitude in the thugs Joong-ki dispatches to kill Sun, and thus decides to help her fight back.
- Heroic Sacrifice: Opts to return to prison after having a taste of freedom, rather than burden Sun on her quest for revenge.
- Improvised Weapon: Kills one of Joong-ki's thugs with a broken mob handle.
- Never Mess with Granny: Besides poisoning her husband, she also kills one of Sun's would-be assassins who was hanging her, single-handedly thwarting their almost successful attempt.
- The Old Convict: Is older than most of Sun's fellow inmates and acts as something of a mentor to her.
- Til Murder Do Us Part: Poisoned her husband and is in prison for it.
- Til Murder Do Us Part: She's in prison for killing her husband, like Min-Jung.
Detective Mun Kwon-Ho
A detective from Seoul Metropolitan Police working on Sun's case.
- Amazon Chaser: Sun's ability to kick his ass every time they fight only makes him more interested in her.
- Dating Catwoman: Played with. Technically Sun's not really a criminal, but she's being hunted by police after escaping jail. Despite having the obligation to arrest her, Mun believed her when she told him that her brother was the real crook.
- Fair Cop: A handsome policeman in tight clothes who falls in love with Sun.
- Forgotten First Meeting: He actually fought Sun in a taekwando competition when they were younger (she won, of course), but neither of them remembered at first.
- Meaningful Name: A bit of a pun here, as he is the cool and jovial Mun (moon) to her quiet but intense Sun, although Mun is technically his family name while Sun is her given name.
- Offscreen Moment of Awesome: Thanks to the story plans after Season 2 having to be squeezed into one final movie, he ends up taking down the entire Government Conspiracy Joong-ki is involved in without the cluster's help as they're busy saving Wolfgang.
- Only a Flesh Wound: Somehow survives a bullet to the gut, fired by Joong-ki as he prepares to arrest the latter for money laundering.
- Sympathetic Inspector Antagonist: He tells Sun's master that "something stinks in the story of her escape" and leaves his card, willing to hear her side of the story. Mun suspects that Sun's brother is the actual criminal and Sun might have been framed. He is even open to Sun's account of her fathers death (being killed by her brother's mooks, which contradicts the official conclusion that he committed suicide) and asks her to make a statement about this on the record. In their last meeting he promises to let her go if she wins a physical fight with him. The next time she sees him, he is about to arrest her brother.
- Deadpan Snarker: The only thing she hates more than rhetorical questions? Stupid rhetorical questions.
The boy Sun fought in her last tournament as a teenager, with whom she lost her virginity.
- Graceful Loser: Makes a point of finding Sun after he lost their bout to tell her it was an honour to have faced her in the ring. It's this act of compassion, humility and recognition which compels her to have sex with him.