Tsukasa is the only daughter of two police officers; upon their deaths in investigating the death of the Kuryugumi boss, she becomes involved with the next boss of Kuryugyumi, Ryuji, her classmate for the past eight years. She was raised as a boy because her mother saw too many women at crime scenes, and wanted to shield her from the excessive sexual mistreatment of women in this era. As the child of two cops, she despises corruption and cruelty, and wants to be a cop herself one day.
She has an extremely happy and bright personality; she is an optimist and thinks that the world is a crazy place, but thinks that she can do her part to make it better. She was trained to fight by her parents, and subsequently, at the start of the story, she is already an excellent fighter and is rarely defeated in a fight. (She fights with a chain whip that ends in a handle that can alternately be extended into a blade.) Incidentally, she also hates the yakuza, citing them at fault for many of the wrongs of the world.
Although, Tsukasa dresses up as a boy for most of the story (she has a chest protector that flattens out her breasts), Tsukasa is actually a very attractive female. She is tall and has an excellent figure, so when she dresses in female clothes and wigs (which she calls it "cross-dressing", since she thinks of herself as a man), looks much more mature and is often the subject of catcalling and other sexual overtures. Despite this, she is very naïve about other people's romantic interest in her and her own growing love for Ryuji.
Tsukasa and Ryuji have attended school together since kindergarten. When she was eleven years old, Tsukasa slipped on a river bank and fell in; due to hiding as a boy, she never attended swimming class and thus nearly drowns. It is Ryuji, who was watching her from the bridge, that jumps in and saves her, giving her CPR and subsequently, discovers that she's female. Ryuji is thus aware of Tsukasa's true gender from the beginning of the story.
Tsukasa has three brothers: her supposedly fraternal twin, Toshiyuki (14), her younger brother, Shohei (13), and her older brother, Takuma (16). After their parents' deaths, Taku drops out of school and works as a casino gambler, while Shohei and Toshiyuki work at a gay bar (all of these professions being illegal due to their age).
Tsukasa later found out that she is the adopted daughter of the Kozukis; she was in actuality the daughter of Wakasa Ayabe and the man that Wakasa was seisai to, the yakuza leader of Hougougumi, which after the deaths of Wakasa and her husband it fell apart. Wakasa gave her daughter to her friends, the Kozukis, along with the kagi to the drug, shortly after Tsukasa's birth (Tsukasa does not remember her at all), knowing that she was going to die. Tsukasa finds inklings about her true parentage after Ryuji was shot and at the hospital,and it was confirmed by Wakasa's former bodyguard.

As the Sandaime - third generation leader - of the Kuryugumi group, he has been raised with the constant goal of succeeding. He rarely shows his emotions on his face, and in fact, as long as Tsukasa can remember, has been an excessively gloomy and sober child. Though not obsessive about exacting justice in the way Tsukasa is, he has his own moral code and holds himself to high standards of behavior, if not society's.
Though Tsukasa is his bodyguard, she once wonders if he really needs one, as Ryuji is skilled at karate, kendo, judo, aikido, and shooting. He is additionally always well-armed (he fought Shiva ((Tsukasa's true uncle who had his memories imprinted on a core and survived death)) with a knife embedded in his watch) and an excellent fighter, though Tsukasa generally fights the most central battles in the story.
His mother died giving birth to him, and his raising was given over to Toshiyuki Kamojima, a lower-ranked yakuza whose pregnant girlfriend had recently been murdered. His own father loved him, but felt that distance was necessary in raising the next-generation leader, and kept generally away from Ryuji in his formative years, leaving Kamojima as his father-figure.
Ryuji is intelligent, cynical, and manipulative; he is in some respects very Machiavellian, but is truly loyal and does what he can to be kind to the people he cares about, though that is a very short list. Alternately, he is not at all hampered by Tsukasa's naïveté, as he is fully aware of his attraction to Tsukasa from the beginning. That said, he can truly relax around Tsukasa; she is one of the very few to see him sleeping, and his bodyguard comments to Tsukasa that around her, Ryuji actually looks his age (just fourteen). He enjoys tormenting and teasing her - ostensibly because she is an unusual creature - but loves her very much. Later in the story, Tsukasa is the one to see him cry and comfort him after Kamo-san was killed by one of the Ultimate weapons.
Despite his relationship with Tsukasa, however, Ryuji is engaged to Asago Sumon, the daughter of one of his lower bosses, who has essentially been raised for the role of being his wife. Ryuji cares for Asago, but Asago does not discover until much, much later, that it is the way a brother cares for his sister, while Asago is genuinely in love with Ryuji. His engagement to her is to prevent clan conflict (since the clans under Kuryugumi all accept Asago as an appropriate candidate) and also for her sake, as he desires to make her happy. However, he cannot stop himself from pursuing Tsukasa, causing great tension among the love triangle.

Tsukasa's older brother. He's not too happy about his sister being friends with Ryuji. Dropped out of school to help with family expenses. Works as a dealer at a casino. Very reliable and is family oriented. Friend of Onda. Highly recommends Akira as a boyfriend to Tsukasa... Knows a deep dark secret about Garyukai and is trying to prevent Tsukasa from being involved with them. Will forever act as big brother towards Tsukasa even if they're not blood relatives.

Tsukasa's twin brother, although in the first story, he was introduced as Sho's twin. He's the younger twin and has no problem with Tsukasa getting along with Sandaime. Works as a host of a gay bar. Has medium dark hair. Still cares for his sister though he learns the truth.

Tsukasa's youngest brother. The cutest and probably the most spoiled. He too wouldn't mind seeing his sister getting together with Ryuji. Also works as a host of a gay bar. Has light coloured hair. Does not plan on abandoning Tsukasa, even if things aren't so pretty...

The father of the 4 Kozukis and the person that Kise Akira admired. Was a member of the police special task force known as GRAVE that dealt with the rising crime. Was killed while chasing Hizakigumi while off duty, a few days after Ryuji's father was killed. The one who trained Tsukasa when she was little. Had a strong sense of justice. The inventor of Tsuaksa's protector. He knew Ayabe Wakasa and even called her "Waka-chan".

The mother of the 4 Kozukis and the one who decided to raise Tsukasa as a boy rather than as a girl. Also a member of the police special task force GRAVE. Was killed while investigating Hizakigumi. Has orange hair (!!?). Was entrusted some deep secret of Garyukai plus... see episode no. 66 for details. Seems to have had contact with Wakasa. Had a strong sense of justice. Taught Tsukasa to be strong.

Ryuji's late father who was killed by Odawara. Also known by his title Nidaime (the 2nd generation). Looks almost exactly like Ryuji. Was admired much by Kamo-san. Had a promise with Kaya that Ryuji fulfilled. Took personal interest in Kamo-san's intent on getting revenge on Hanawa.

No longer Ryuji's fiancee (seisai, literally translated as the good/right/holy wife). She was aiming to be like Durga, a legendary sort of female figure, who acts as her husband's right hand woman. Only daughter of Sumon, the head of the Silver Dragon Clan, the head clan under Kuryugumi. Asago is jealous that Ryuji's time is partially occupied with Tsukasa (and not her). She's quick to show her temper and is reluctant to trust Tsukasa as she is a katagi. Like Ryuji, she's armed with a gun, and she's quite good (she can use two at once), although she's not that great at physical fighting. Trusts nobody except Ryuji. Finds out (to her dismay) that Tsukasa is a girl. Has contemplated suicide but changed her mind after meeting with Munakata. After meeting up with Tsukasa again she finally accepts it that it's Tsukasa and not her who can make Ryuji happy. Has some feelings towards the scarred cop?

Ryuji's main associates and bodyguards. Kamo-san is the older of the two and has served Nidaime, Ryuji's father as well. He probably knows Ryuji the best out of all the Kuryugumi members, and is usually seen with a smile on his face. He would very much like to see Tsukasa and Ryuji get together, thinking that Tsukasa would make a good ura no seisai literally the hidden seisai. A father like figure to Ryuji, since he practically raised him. Has a dark past as seen in ep. 85. Made a grand exit from the manga in episode 90 [sniff!!]

Bun-san has more of a temper than Kamo-san, and is the one with the glasses. More of a brotherly figure contrasted with Kamo-san's fatherly nature. Can't see Tsukasa and Ryuji getting together but accepts that Tsukasa is very capable of the position of seisai. He sucks at using his gun (according to Tsukasa) and is also Ryuji's main chauffeur and intelligence expert. He's not fond of children. Both he and Kamo-san the few people who know that Tsukasa's a girl and they also know about her ties with Wakasa.

Daughter of Shibata, oyabun of the Gold Dragon clan under Kuryugumi. Looks like a female version of Ryuji with long wavy light coloured hair and really big breasts. Has an ego the size of the universe, but fell in love with Ryuji at first sight though she's much older than him. This caused her to challenge Asago in her position as Durga. Can handle a gun but is not very good. Loves to show off her wealth and her body. Glares a lot and treats other people especially those "inferior" to her as scum.

Two younger members of Kuryugumi who get into trouble often. Shigaraki has light coloured hair and has his left ear pierced a couple of times. Muko has dark coloured hair mostly swept back. Both do not get along well with each other and both detested Tsukasa at first. Even when they team up, they end up fighting... Both were disowned by their parents before finishing elementary school, passed around to different relatives, then became a runaway at 13. Were literally picked off the street by Ryuji 2 years ago. Very loyal to Ryuji.

Doctor of Kuryugumi's private hospital (inside Kuryugumi's main house). Was ordered by Ryuji to discover the how Paramelt works and to "cure" Tsukasa. Looks kind of like an older version of Tsukasa. Is somewhat worried about Tsukasa's future as she is so boyish. Was somewhat surprised to discover that Tsukasa is female, but is keeping the secret. Likes to tease both Ryuji and Tsukasa especially about the © between them. Is trying to convince Tsukasa to be a girl.

A cop who kept appearing whenever the police were called. Admired Tsukasa's father, Kozuki Yutaka, and decided to become a police officer after meeting with him. Thought he was gay since he found Tsukasa attractive... He's really tall and unbelievably strong. Funny and honest. Hates the yakuza, especially Kuryugumi who he thinks is responsible for Kozuki Yutaka's death. Seems to have a bit of a dark past. A member of the GRAVE section of the Control Police. Munakata's partner. One of the few people that know that Tsukasa is female, and has an interest in her... even though he's much older. Views Ryuji as a rival.

A member of the GRAVE section of the control police and is currently Akira's partner. Usually cool and calm. Has a scar running down the right side of his face. Appears to have a tendency to become as violent as the criminal he catches. Has to be stopped from killing the criminal according to other colleagues. When he changes to his "violent" side, all colleagues stay clear of him in fear... though it's supposed to be his partner's (Akira) job to stop him... Has a very sweet side to him. Claims that he lives only to protect women. Known to use his police cruiser as a mobile hotel... He's the same age as Akira but looks like an oyaji according to Asago. Has a soft spot for Asago. Happens to be Nakamura's favourite character.