Kaguya Sumeragi (皇神楽耶, Sumeragi Kaguya), 14 years old (15 at R2), is the young head mistress of the Kyōto House and a supporter of the Black Knights. She is also a close friend of Empress Tianzi of the Chinese Federation and the cousin of Suzaku Kururugi.
Kaguya has black hair (her hair is kept in two ponytails during the first season) and green eyes.
She wears a pink-ish blouse that has detached sleeves along with a red miniskirt. In the second season, she often wears a long pink dress with red details.
Kaguya is shown having a great sense of responsibility and generosity, showing great care and loyalty towards her subjects and allies, along with being such a noble figure among the Houses, allowing her to obtain such high influential around her. Even C.C., as cold as she was, acknowledged Kaguya as being genuinely kind. Kaguya is also very familiar within the Leadership of The Black Knights, mostly due to her admiration for Zero since his debut. Kaguya has wished to have his hand in marriage. Nothing anyone says contrary to this desire seems to faze her, including the suggestion that Zero might having relationships with other women - formed from the idea that Kallen Kōzuki, C.C. and Zero had escaped capture and remained together in secret for a full year - to which she later decides that "A true hero enjoys physical pleasures" and proceeds to suggest that she, Kallen and C.C. are Zero's harem.
However, this is merely a façade of a young maiden's beliefs and dreams regarding the power of dignity. Being born into a high-status family, Kaguya had been spoiled by her authority figures during her childhood, until an incident involving Lelouch vi Britannia inspires her about the nature of desires and arrogance. Therefore, Kaguya has constantly fantasized that anything is justified as long as people pursue peace, in turn creating a proper cycle and unlimited opportunities for humanity, including herself. This personality flaw has been heavily remarked by Lelouch, eventually resulting her overwhelming downfall against the tyrannous actions from "The Treacherous Emperor".
Kaguya met Lelouch and Nunnally during their childhood at the Kururugi Shrine, and is Suzaku's cousin. A Sound Drama set in the second season reveals that she was engaged to Suzaku, and was cruel to him because he wouldn't allow her to play with him and his friends at the behest of Taizō Kirihara. Becoming frustrated when Suzaku again refuses to play with her and insists that she studies, she runs off into the nearby forest. There, she runs into Lelouch, who she mistakes for the "demon of the forest", and he permits the misunderstanding to continue. Fearful, she attempts to secure her safety by using the Sumeragi name to intimidate him, which is met with scorn, but he permits her to leave. At this, she admits that she does not want to return, because they do not let her do the things she desires, but cannot be anything other than a Sumeragi. Lelouch insults her lack of ability, saying that none would desire such a woman, and that she has no merit. Crying, she flees and runs back to the shrine, and apologizes to Suzaku, who comforts her and says that he'll ask his father if she can play with him. At the end of her tale, she says that she believes that she's changed since then. When Zero suggests that he may be a demon, she says that is fine, because the important thing is that she chose him herself.
She appears in the first season during a Kyoto House meeting, hidden behind a screen, and properly introduces herself to Zero just before the Battle Of Tokyo. She offers to be Zero's wife, claiming that she is a goddess of victory, but is rebuffed, as he says that he sold his soul to a devil, and cannot be a goddess's friend.
She is the only living member of the Kyōto House following the Black Rebellion, having managed to escape to the Chinese Federation until Zero's return one year later. She is aboard the Black Knights' submarine when it reinforces Zero, pleased to meet him again. Kaguya later reunites with Suzaku after blocking Schneizel so that Zero won't use his Geass. The two talked and Suzaku responded negatively to her remarks, such as about the Six Houses Of Kyoto's deaths and Zero's rescue at the Orange Incident. She is later seen during the kidnapping of Empress Tianzi to help her see the outside world that always wanted to see.
After the formation of the United Federation of Nations, she became the representative of the United States of Japan as well as the First Chairwoman of the U.F.N. Supreme Council. During the assault on Area 11, Kaguya is present on Li Xingke's command transport. After receiving word of Zero's death and the armistice between the Black Knights and the Britannian forces, Kaguya returns to the Ikaruga to negotiate the armistice terms. Though she is deeply saddened by the news of Zero's death, she remain strong in her resolve and intends to utilize Zero's death as much as possible for the benefit of the U.F.N. She is present when news of a rebellion within the Emperor's forces near Kaminejima arrives. Believing that only one person could cause such chaos, Kaguya decides to follow Schneizel to the island. She also postpones their meeting, needing to confirm several details first.
When Lelouch is crowned the Britannian Emperor, Kaguya and the rest of the Black Knights are visibly stunned. After Lelouch consolidates his power in the following month, she chairs Britannia's entrance into the U.F.N. at Ashford Academy. She and the others easily see through the fact that Britannia's large population would give it a supermajority vote in the UFN, effectively giving Lelouch control of the organization, and try to get him to either limit his vote or allowed the Britannian Empire to be disbanded. Unfortunately, Lelouch already had Suzaku sneak though the surveillance, allowing the Lancelot Albion to infiltrate the school grounds and hold Kaguya and the U.F.N. officials hostage with its Super VARIS.
Later, Lelouch takes her and everyone else present hostage aboard the Avalon to force the issue. She, along with the other hostages, are later released by Xingke. After being freed, Kaguya and her men catch C.C. atop the Lancelot Frontier's cockpit, floating atop the Pacific, informing her that Suzaku was supposedly killed. Kaguya is later arrested by Lelouch, and she is slated for public execution along with Tianzi, Xingke, Tohdoh, Ohgi, Kallen, Schneizel and others. They're all freed when Lelouch is killed by Suzaku, him having taken the role of the new Zero. She was one of the few who realized Lelouch's true intentions after his death. She is last seen in Ohgi and Viletta's wedding photo.
Despite her age and physique, Kaguya is wise and skilled beyond her years, managing to score the second highest total attributes rating among the core members of the Black Knights, behind Kyoshiro Tohdoh. Specifically, she is the most charismatic member of the Black Knights, second most loyal and second for most intelligence matching Diethard Ried and behind Rakshata Chawla.
Appearances in Other Media
Code Geass: The Manga
Contrary to her wiser and more loyal personality in the anime, Kaguya ends up playing the role in leading to the Black Knights' betrayal of Lelouch vi Britannia instead of Kaname Ohgi and Diethard Ried. She becomes the Prime Minister of Japan instead of Ohgi in the end. She does, however, display similar attractions towards Zero like the anime. She supports the Black Knights in the first part of the storyline instead of Taizō Kirihara.
Nightmare of Nunnally
Kaguya's role in Nightmare of Nunnally is the same as the anime of being part of the Six Houses of Kyoto but is different since there are no United Federation of Nations. She appears when Zero makes conduct with the Kyoto Group Funding as well as when she and Taizō Kirihara supports Euphemia li Britannia's position for the throne to Cornelia li Britannia and Gilbert G.P. Guilford. She appears again when Kallen Kōzuki in her Guren Flight Enabled Version during the chaos over all the areas due to the arrest of all Viceroys declared by Charles zi Britannia and Rolo Vi Britannia. Her final appearance would be after the final battle along with Kaname Ohgi who is the new leader of the Black Knights, Kallen, and Shinichirō Tamaki saying that Zero has been declared dead at the battle and that they will never get the chance to know his identity as well as his reason for fighting but regardless Japan is free and they have to make negotiations with Britannia by then.
Nunnally in Wonderland
In Code Geass: Nunnally in Wonderland, Kaguya plays the role of Tweedle Dee. When Nunnally vi Britannia reaches a three way fork in the road, Tweedle Dee and Tweedle Dum (Empress Tianzi) appear in front of her. When Nunnally asks them which path leads to the exit, they both point in different directions and then begin arguing with each other over random things.
- (To Zero) "Once you have won this war, you will need a wife someday, right? For you to have a life where you cannot reveal your identity to the world, I believe that there will be someone who can calm your soul."
- (To Zero) "You want father my child? Im am not in objection."
- (To Kallen Kōzuki) "Heroes are always ladies' men,after all.You need to take into account for the fact he is a grown man."
- (To C.C. and Kallen) "The three of us who support Master Zero...Oh! That makes us his three court ladies,right?"
- The name Kaguya means "Shinto music" (神楽) (kagu) and "question mark" (耶) (ya).
- Kaguya's surname Sumeragi means "emperor" (皇).
- The poem titled "Hitomi no Tsubasa" that came with the Code Geass Complete Best CD reveals that Kaguya mourned Lelouch vi Britannia after his death and wondered about what would have happened if she had known the true Lelouch earlier on.
- Kaguya's character was inspired by Princess Kaguya from the Japanese narrative folklore tale "The Tale of the Bamboo Cutter".
- Kaguya's voice actress, Mika Kanai, also plays Tiffa Adill from After War Gundam X who is almost the same age as Kaguya.