Kallen Stadtfeld (カレン・シュタットフェルト, 紅月カレン)

Background

'Kallen Kōzuki' (紅月カレン Kōzuki Karen) is one of the tritagonists in the anime/manga series Code Geass. She is officially known as 'Kallen Stadtfeld' (カレン・シュタットフェルト Karen Shutattoferuto), and goes by this name at school, but prefers her mother's maiden Japanese name during her revolutionary (now military) activities.

Kallen is a strong-willed, determined, loyal, and brave individual who can also be quite short-tempered, forceful, and somewhat impulsive. Despite her uncompromising attitude, Kallen is quite sensitive, compassionate, and genuinely gentle.

While being both Japanese and Britannian, Kallen could live everyday life. However, she refused to fully accept her Britannian side as it would mean abandoning her Japanese friends, people, and self, thus making her one of the few selfless characters in all the series. On multiple occasions at the beginning of the series, she had claimed that she hates Britannians. However, that was an exaggeration, as Kallen caring about Britannian civilians on multiple occasions.

Her father is a Britannian noble who comes from a prestigious family. Since his legal wife, Mrs. Stadtfeld, could not bear any children, Mr. Stadtfeld requested Ms. Kōzuki to adopt Kallen into his household as his heir formally. Since her daughter would benefit from being a Britannian noble, Ms. Kōzuki accepted his request without Kallen's consent, much to her displeasure. Though Stadtfeld's wife ordered her never to see her daughter again, Ms. Kōzuki refused, fighting hard to be hired as a maid in the Stadtfelds' household to remain by her daughter's side, something that Kallen was unaware of at that time.

Both Kallen's stepmother and mother live with her in the same house. Still, her biological mother was often mistreated by both her stepmother, the other maids (who were all pure Britannians), and even Kallen herself after their relationship became strained. However, she would try to discreetly help her mother at times but still stayed away from her.

After this incident, Kallen returns to school for the time being. She returns to class with a fake persona of a frail girl. After Lelouch discovers that Kallen, one of the terrorists he helped in Shinjuku Ghetto, attends the same school, he attempts to confirm his suspicions. However, Lelouch's unfamiliarity with his Geass causes him to reveal knowledge of the Shinjuku incident to Kallen, leading her to suspect him of being their unknown benefactor.

With the formation of the Black Knights and Zero's increasing number of victories over the Britannian forces, Kallen comes to admire him greatly.

During one of the Black Knights operations to stop the drug distribution, Refrain, Kallen notices her mother as one of the people using it. She attempts to save her using her Glasgow, but a corrupted member of the Britannian police force employs a Knightpolice to kill Kallen. During the battle, Kallen realizes that her mother decided to stay in the Stadtfeld household to be with her and calls herself a fool for not recognizing her mother's love towards her.

After losing her Glasgow, Zero gives Kallen the newly-developed Guren Mk-II to replace it.

Due to the immense growth in Black Knights, Zero announces the chain of command and gives Kallen the position of being captain of the Zero Squad, Zero's force.

After Scheizel's unexpected appearance with the Avalon at the Shikine Island battle, Kallen appears to be alive and found by Suzaku, who arrests her for being a member of the Black Knights. They spent time together discussing their life and Ashford until things became heated talking about their ideas, only to be shocked by the truth of Genbu's assassination and that Suzaku is willing to atone for it. The following day, Kallen and Suzaku run into Zero and Euphemia. The floor below them collapses, giving Zero and Kallen a chance to escape with the Gawain.

At the end of the first season, Kallen reveals her identity to the students of Ashford Academy when the Black Knights occupy it as their base of operations, convincing the student council that Black Knights will not harm them. When Zero abandons the battle to rescue Nunnally, Kallen follows him. She witnesses his confrontation with Suzaku and learns about his true identity, the truth about the massacre of SAZ, and his Geass power. Kallen was also shocked to hear that Lelouch admits that he used the Japanese, including her, for his scheme. She flees in shock rather than aiding Lelouch to deal with Suzaku.

One year later, Kallen is still part of the Black Knights, but due to revealing her identity has had to leave Ashford Academy. Her memory was one of those erased from Lelouch's mind by Charles Zi Britannia, although the other students are still aware of her existence. Along with C.C., she is one of the first members to know Zero's identity and secret power, bringing up to speed by C.C. in the interim.

During the operation to kidnap Nunnally vi Britannia, Kallen was transported to Area 11. Kallen receives an upgrade for the Guren Mk-II, giving it flight capabilities and an upgraded radiation arm.

During the Black Knight's attempted kidnapping of Empress Tianzi, Kallen is captured by Li Xingke in his Shenhu. Lelouch, visibly stunned, swears that he'll rescue her. Touched by Lelouch's words, Kallen calmly waits for him.

After the High Eunuchs turn to Schneizel el Britannia for military support, Kallen is turned over to Suzaku along with the Guren. She is sent back to prison in Area 11 and subsequently transferred into a more comfortable solitary cell by Nunnally. Later on, Suzaku approaches her after Shirley's death, intending to use the drug Refrain to find out if Lelouch has become Zero once again, but cannot bring himself to do it because he refuses to stoop to Lelouch's level. In retaliation, she beats him severely during their next meeting when Suzaku tries to apologize.

During the second battle of Tokyo, Kallen is rescued from captivity and returned to the Guren (complete with a pilot suit brought by Sayoko). Using the new Guren, she decimates the Britannian forces. She then fights Suzaku, easily breaking through his defenses and bringing him to the brink of death. In doing so, however, she activates his Geass command, forcing him to survive by firing the F.L.E.I.J.A. bomb. She dodges it, and the bomb hits the government building, destroying a fair portion of the Tokyo Settlement.

After Kallen returns to the Black Knights and Zero's identity is revealed, she tries to defend him. When the others don't listen, she asks what she means to him, expressing a willingness to die then and there as long as it's with him. Lelouch, thinking that he had lost everyone he held dear to him, refused to have her die with him and lies and calls her a tool, but then whispers that she should live on without him within earshot.

Following Lelouch's escape, Kallen tries to protest how Ohgi and the others have discarded Zero so readily despite all that he has done for them. However, they refuse to listen, still angered at the idea that they merely used as pawns. As the Black Knights move to assist with stopping the rebellion within Emperor Charles' forces, Kallen thinks to herself that Lelouch needs to live, as she cannot move on before getting an answer to her question. When Lelouch is crowned as the Emperor, Kallen and the rest of the Black Knights are visibly stunned.

After Lelouch's declaration that Britannia will join the UFN, Kallen escorts him to the meeting, giving orders to the Black Knights beforehand to gun her down if she appears to be under the influence of Geass. Lelouch gets her to take the long route, giving them the chance to speak in private. Kallen recounts their history, then asks Lelouch what he intends to gain by becoming Emperor, as well as what she means to him. Lelouch remains silent, so she kisses him to show her feelings. When he doesn't react, she bids him farewell. Lelouch does the same once she can no longer hear him.

After the Black Knights side with Schneizel, Gino agrees to fight despite that he would be going against Britannia, telling Kallen that he understands her feelings a little. Kallen is stationed in the front lines. She breaks away from the mainline to try and reach Lelouch but is called back. Kallen breaks into the Avalon and attempts to kill Lelouch, with tears in her eyes as she does so, but is stopped by C.C. Kallen easily defeats C.C. and, with the help of Gino, proceeds to the Damocles for a final confrontation with Suzaku.

After a fierce battle, Kallen manages to land a decisive blow on the Lancelot before losing consciousness. Gino rescues her while the Lancelot explodes. After the war, she is taken along with many others who rebelled against Lelouch to be publicly executed, where she witnesses Lelouch's death by Suzaku disguised as Zero. Understanding Lelouch's plan, she screamed as Lelouch was stabbed. However, she still stated with Tohdoh that Suzaku was "Zero."

(Sources: Code Geass Wiki, Wikipedia, Heroes Wiki)