Lucy - Number 7, or Lucy, can be described as nothing more than a confused killing machine. When Lucy was a child, she lived with another girl and three boys that always bullied her. Eventually, Lucy found a small puppy that she could befriend and did so, feeding it bread every night. When the girl started being friendly with Lucy because of the bullying boys, Lucy told her about the dog, but to not tell the 3 boys or else it would be bullied by them as well.

One night, Lucy thought she felt something moving in her body. This was the first time she had felt the "vectors" (invisible arms that come out of the portion of the back closest to the neck). The next day, the three boys decided to bully Lucy again,, but this time they had the dog. Lucy pleaded them not to do anything to it but instead, they beat it to death with a vase. The boys let it slip that it was the girl that had had told them about it, and in a fit of rage, Lucy killed all four of them right there with her vectors by cutting off their necks. A few days later, Lucy met a boy named Kouta. At first, Lucy did not want to befriend him because of how she was betrayed by the girl, but in time, Lucy and Kouta became good friends. They played together, had fun, and went to the zoo.

At the trip to the zoo, Lucy was talking to herself when she accidentally said "I need to find a place to stay. Maybe I should kill some people to get a place." (or something like that) Lucy then questioned why she even thought of killing another person when a voice inside her head said "because you think it's fun." On the way back from the zoo, Lucy learned that Kouta couldn't take her to a festival the next night because he had promised to take his cousin beforehand. The evil voice inside Lucy's head asked whether it was a boy or girl and told Lucy that she should kill Kouta right then to have to worry about the pain of Kouta being with another girl. When lucy came to, she found herself strangling him. before they left, Lucy asked if his cousin was a boy or a girl. Kouta decided to spare her feelings and told her it was a boy. relieved, Lucy went and killed a family to stay at their place.

Lucy thought that it would be right to see Kouta off at the festival and so she went there to say goodbye one last time. When she saw Kouta was with a girl, her entire world froze. She flashed back to when the girl had betrayed her before and decided she was sick of it. The evil voice inside her head (always sown as a wrapped up girl with only one eye showing) unwrapped her bandages to reveal it was Lucy. She told Lucy that all humans are nothing mor than let-downs and that all of them should be destroyed. Lucy and her evil voice became one at that moments and all at once, Lucy killed the six people standing around her at once. Confused, people ran amuck. One woman tried to help Lucy but she killed her too. On the way back to Kouta's house from where he was staying with his cousn, Lucy killed both Kouta's sister and father, saying that she was going to go after Yuka next. She was caught by a member of a secret research institute and eight years later, she escapes but when she is about to succeed, a bullet strikes her head and she ends up losing conscience.

Every now and then, Lucy comes back into her own mind from Nyuu and she gets very hostile. She also begins to redevelop her original feelings for Kouta as the series progresses. Just as the soldiers begin to fire their guns at Kouta and Nyuu at the end of the series, Lucy saves them both with her vectors. This is odd to everyone but Kouta since they thought Lucy was a killing machine. When the asisstant director tries to explain that Lucy and Nyuu are two different people, Lucy cuts her in half with her vectors, killing her. She then proceeds to kill all of the soldiers there except Mariko, who had been taken away.

Lucy fights Mariko and loses and afterwards, she tells Kouta that she regrets what she did to him. The only reason she lived up that point and escaped from the institute was to tell him that she was sorry for what she did to him. On the way out, Lucy surrenders her vectors to the air and is killed by the Special Assault Team.
_____________________________________________________________________________________
Nyuu - Nyuu is almost the exact opposite of Lucy, except is the same person. When Lucy got shot in the head after escaping from the institute, she lost conciousness and regain conciousness as Nyuu. Nyuu, for lack of a better word, is almost too stupid to do anything. She is fine to walk, barely, but in the first episode, before anything is taught to her, she can't eat, bathe, or even go to the bathroom right. Nyuu was taken in by Kouta, but when things started looking a little perverted from Yuka's point of view, she moved in to help take care of her.

Nyuu sees things through a different view than everyone else. if someone looks sad while doing something, she relates the two objects together and fixes the situation. The same goes for happy. Every now and then, Nyuu snaps back into Lucy's mind and things start to work a little bit differently than what was previously going on. Nyuu may seem helpless at one moment, but then switch into Lucy's mind and kill a few people to even things out. Of course, Luccy and Nyuu don't know the other exists and according to Lucy, switching over to Nyuu is just like blacking out. Eventually, Nyuu learns some new words and starts to get better at everything she is taught by Kouta, Yuka, and Mayu.
_____________________________________________________________________________________
Kouta -Kouta is an 18 year old who is renting out an inn from Yuka's parents as long as he is able to maintain its condition. Kouta has what some would call a "soft spot" for girls in trouble and is always willing to help out anyone who might fall into said trouble. Kouta originally finds Nyuu unconcious on the beach and he is the one who decided to take her in. Kouta has repressed his past due to traumatically witnessing the death of his younger sister, Kanae, and his father. Both were killed by Lucy. This is why, until the last few episodes, Kouta does not know Lucy at all, despite being with her and having fun with her in his past (see Lucy).

When Lucy starts killing everyone in front of Kouta after the confrontation with Mariko, Kouta sees Lucy for who she really is, and not Nyuu. Kouta then suddenly remembers everything. Having fun with that girl way back when, and then he flashes back to after the festival. he, his dad, and sister Kanae are on the train going home. Kanae says that a girl with horns killed all the people at the festival and it wasn't a bomb like many said it was. Kouta calls her a liar but she defends to the death what happened. Lucy the appears from the train and kills Kanae and Kouta's father right in front of his eyes. When Kouta asks why she did it, "I thought we were friends!" Lucy replies, "The only reason you're still alive is because we are friends." Kouta continues to watch Lucy kill the soldiers and rememberes that she said "If one day I start to kill many people, I want you to kill me." Because of what Kouta witnessed when he was a child, he was hospitalized for a year, where he completely supressed the memories until he could no longer recall them.
_____________________________________________________________________________________

Yuka - Yuka is Kouta's cousin and she is in love with him.This causes some conflict between her and Kouta because he pays a lot of attention to Nyuu. In Japan, cousin marriage is not frowned upon like it is in North America. Most who watch the series are unaware of this and tend to see this as crazy incest loving, whereas in Japan, this is just regular incest loving. Kouta took Yuka to the festival when they ere kids instead of Lucy, which triggered her incredibly violent ways.

_____________________________________________________________________________________
Mayu - Mayu is not introduced to the story until the 2nd episode when she witnesses Lucy torture, but not kill, Bando. Mayu is a 13 year old (she turns 14 around episode 5 or 6) runaway. When she lived at home, her new stepfather made her remove her clothes many times. It was assumed, not actually shown but hinted that, she was raped by him as well. When Mayu's mother would not step in, saying that she prefered her husband over her child, Mayu went over the edge. The next time her stepfather asked her to remove her clothes, Mayu simply said no and ran away. She then finds a small puppy she names Wanta and becomes less lonely. She witnesses Lucy and Nana's first battle and later in the series, becomes friends with Nana. She is taken in by Kouta and Yuka and decides to live with them.
_____________________________________________________________________________________
Nana - Nana, like Lucy, is also a diclonius, but is very much the opposite kind of person. Nana's "father" (director kurama) sends Nana to retrieve Lucy for him and that she would be rewarded when she got her back. However, she failed. Nana does not wish to harm anyone who does not wish to harm her, and just hates fighting in general. Nana's vectors are much longer than Lucy's which gives her the upper hand when they fight, but due to Nana's personality, Lucy takes the opportunity to cut off both her arms and legs. When Nana returned to the institute, she was supposed to be killed because she was useless, but instead, Kurama made fake arms and legs for her which are controlled by her vectors, and set her free. Nana became good friends with Mayu in the middle of the series and was adopted into Kouta's inn by both Kouta and Yuka. Nana has the ability to temporariliy disable another diclonius' vectors by running hers through their pineal glands. This causes them to stop. She does it to both Lucy and Mariko. When Kurama and Mariko die, the researcher who triggers the bomb aims his gun at Nana, but Lucy cuts off his head and tells Nana to go live in peace with Kouta and Yuka.
_____________________________________________________________________________________
Director Kurama - Kurama is the research director at the institute that held Lucy. He is also the "father of Nana. During his earlier years at the institute, Kurama was in charge of researching the diclonius' vectors. Number 3, or Sanban, was the test subject. When she attempted to escape, she decided to look for Kurama first and to kill him for all the suffering she went through for the research. In her attempt, she touched both Kurama and another researcher with her vectors, giving them the vector virus. Sanban was shot in the head moments before she was about to kill Kurama. Her last words to him were "I need to thank you." The 2nd scientist's wife had given birth later on and the baby was a diclonius. It was to be killed by Kurama, who didn't seem to be too troubled by t. When Kurama's wife gave birth to a diclonius as well, he realized that when Sanban touched them withher vectors, she passed them the virus.

Before he could kill their baby, the wife, who had given birth and had to have surgery due to cervix cancer, tried to stop him, but because she was fresh out of surgery the day before, she died of blood loss. Kurama made a deal with the head director of the institute that in exchange for letting his daughter live, he must be indebted to the institute forever. In the final episode, Kurama meets Mariko and decides that because he let her live, so many lives had been lost. He decides that the only true option is to kill Mariko. However, Kurama cannot fire the gun at Mariko because he knows that deep inside, she's his daughter. Kurama accepts that he was not a very good father towards Mariko. He and Mariko both exchange happy feeling toward each other and Kuramam picks Mariko up and takes her out to the road. He then orders the bomb inside Mariko to be blown up. Both he and Mariko die in the explosion.
_____________________________________________________________________________________
Bando - Bando is a member of the Special Assault Team that was sent to take down Lucy in episode 2. Bando is very overconfident in his actions, which leads his arm to be cut off and both his eyes gouged out by Lucy. Later in the series, he is fitted with a metallic hand and man made vision that allows him to see almost as well as he could before. Mayu saves Bando after lucy's punishment to him by calling an ambulence. Later in the series, Bando gives Mayu his number because he doesn't like being indebtted to anyone. When Mayu lets it slip that she knows where Lucy is (Nyuu), Bando threatens to kill her if she doesn't tell him. She gives Bando his number back asking her to save her. Speechless, Bando leaves and finds Nana, who after a short confrontation, agrees to team with him and together, they would destroy Lucy for good. Bando is injured in his last fight with Lucy as well. Why Lucy never kills him is unknown.
_____________________________________________________________________________________
Mariko - Mariko is the diclonius to rule them all, as well as Director Kurama's biological daughter. Mariko has 26 vectors, each with a range of 11 meters. Compared to Nana and Lucy who have 4 vectors of 3 and 2 meters respectively. Mariko is a merciless killer; She is even worse than lucy. However, after she kills one person at the institute upon her release to bring back Lucy, one of the explosives in her arms blow and the researchers tell Mariko about the explosives in the rest of her body. Mariko becomes more tame after this. Because Mariko has never been out of a heavyily protected cell since she was born, she is unable to walk by herself and so he uses a wheelchair.

When she first got to the city, she confronted Nana, and was ordered to kill her. Because she's the only one Mariko had to kill, she decided to have some fun torturing her first. Just as she is going to kill Nana, Kouta arrives and she is ordered to stop. When Nyuu finally arrives as well, Mariko decides to kill Nana against the will of the assistant director, but Nana disables Mariko's vectors and falls into the sea, saving herself.

When Mariko recovers her vectors, she fights Lucy and because she tears off one of Lucy's horns, Lucy is supended in a state of shock, unable to move and unconcious. When Kurama finds Mariko, she knows right away that he is her true father. When Nana calls Kurama "Papa," Mariko asks why she calls him papa, yet she had to be confined to that room for so long. She then begins to attack Nana, trying to get a reaction out of Kurama.When Kurama drops his gun, she stops beating Nana with her vectors and the two of them leave. The bomb inside Mariko is then detonated, killing both Mariko and Kurama.
____________________________________________________________________________________
At the very end of the series, Kouta, Yuka, Mayu, and Nana are eating when Wanta begins to bark. Kouta goes to see if there is a visitor there to see them but all we can see is a shadow behind the door. Before Kouta goes to open it, th broken grandfather clock that Nyuu was always playing with throughout the series begins to chime. It has not ever been said, but there is much speculation that the visitor at the door was Lucy. However, since Lucy was killed, this possibility is deemed as impossible.