|Debut:||Manga Volume 4, Anime Episode 8|
Kouya Sakagami (坂上江夜 Sakagami Kōya) is the Sentouki of the female Zero pair. Until they met, both pairs believed they were the only Zero pair to exist. Both teams are experiments created by Nagisa Sagan at different times, and the female pair is presumably the first generation.
Not much is known about Kouya's background, other than her initial origins. Both her and Yamato Nakano were created by Nagisa Sagan in her series of Zero experiments. Unlike the male Zeroes, Kouya and Yamato were given different surnames. It's stated in chapter 118 that Kouya actually has an adoptive family, while Yamato lives alone.
Kouya and Yamato met when they were younger. The manga does not explicitly state their ages, but the two appear to be around junior high age. During this particular flashback, it's implied that Kouya lives outside of Seven Voices Academy and was brought in to meet Yamato, while Yamato seemed to live at the academy. During their official meeting, Kouya was cold and formal towards Yamato.
When first shown in Volume 4 of the manga, Kouya has been sent with Yamato to defeat Agatsuma Soubi. She is shown departing from her high school, and it's stated that the high school she goes to is prestigious. Kouya appears to have acquaintances at the school, but not close friends. She and Yamato meet with Soubi outside of Aoyagi Ritsuka's school, and they battle him alone, easily defeating him.
During this battle, Soubi states that Kouya's fighting style relies heavily on numbers and calculations and that she's very precise with her spells. It's unclear when Kouya studied at the academy, or if she even did at all, but she's described as stronger than the male Zeroes. Her and Yamato have a close romantic unit relationship, and they're shown kissing and being affectionate towards each other at multiple points in the manga and the anime. Kouya also wears fake cat ears, as hers were presumably taken by Yamato.
After their battle, Nagisa treats Yamato and Kouya badly, even though they won. Kouya and Yamato are told that Nagisa eventually plans on switching out the Zeroes to make a stronger pair, and Nagisa indirectly warns them to not grow too close. This upsets Kouya and when they're ordered to fight Loveless again, they encounter the male Zeroes and are surprised to know of their existence. Kouya attempts a spell that switches the bonds of the Zero pairs, effectively defeating Natsuo and Youji, but causing great psychological harm to herself.
As Loveless prepares for another battle with them, Kouya undergoes more stress stemming from Nagisa and the pressure to win the battle, and she struggles with the idea of being forced to leave Yamato. This comes to a head when during the battle, it's revealed that there's a defect in their line of experiments and that Yamato can feel pain. Kouya forfeits the battle upon learning this, even when Agatsuma Soubi informs her that she'll never be able to fight again if she does.
Kouya then tells Nagisa that she's leaving and breaks things off with her. This upsets Nagisa and Kouya and Yamato prepare to commit suicide together in order to get away from her. They decide to live, though, as a couple.
During chapter 118, Yamato resurfaces in a conversation with Natsuo and informs him that after contacting Nagisa, the two had gone to a love hotel. Yamato had become upset at the prospect of keeping Kouya away from her life and tried to send Kouya home, but Kouya retaliated and stayed. She proposed marriage, and the two are currently engaged and see each other as a familial unit. Kouya still attends high school, while Yamato works, and it's implied that the two are living together.
Kouya is described at multiple points (particularly by Yamato) to be very intelligent. She attends a prestigious high school and does well. In chapter 118, Yamato tells Natsuo Sagan that Kouya is currently taking college entrance exams and that she plans on going to college. Her intelligence is also shown in her battling technique, where she primarily uses numbers and calculations in contrast to Soubi's brute force technique.
Initially, Kouya seems very cold and withdrawn, as shown in her initial meeting with Yamato. However, she clearly warms up to Yamato. Considering Nagisa's treatment of her, it's entirely possible that this is just a coping mechanism to prevent people to get close to her. In Yamato's case, once Kouya accepted Yamato into her life, she attached onto her emotionally and became extremely protective of her. Despite her cold exterior, Kouya was incredibly bothered by the prospect of losing Yamato, and the idea that they were just interchangeable parts caused her a lot of psychological stress.
Once escaping from Nagisa and deciding not to kill herself, Kouya seems somewhat content, though the only shown evidence of this is at the love hotel with Yamato. She seems to be determined to finish school, and she appears to value her relationship with Yamato a lot.
Kouya and Yamato are partners and the Sentouki and Sacrifice of the female Zero team. They are close and in a romantic relationship with each other, and love each other deeply. While Kouya can act annoyed towards her, it's important to note that this is just an act and she does reciprocate Yamato's feelings.
Kouya and Yamato broke away from Nagisa Sagan in Volume 4 after enduring her treatment of them for a long time. They initially planned to commit suicide together, but decided against it.
Kouya is now engaged to Yamato and seems to be living happily with her.
Nagisa Sagan originally 'created' the girls in the first part of her Zeroes series in an attempt to defeat Ritsu Minami. She does not appear to care for them at all and uses them as a way to win a game with Ritsu. While Kouya did not live with her during her childhood, Yamato did and seems to have been badly mistreated by her. Nagisa told the girls that they were just interchangeable parts and that their relationship didn't matter, and put immense pressure on Kouya to win, implying that Kouya and Yamato were nothing to her if they didn't get her results. She's the main cause of Kouya's attempted suicide and Kouya could only be happy once she cut off ties with her.
Despite her treatment of her, Kouya was said to be Nagisa's favorite.
Kouya originally did not know of the second Zero series, and was later informed by Nagisa that they were meant to be interchangeable parts with her team. Meeting them caused a lot of psychological upset for Kouya, due to the fact that it meant she might lose her partner. While fighting them, she furthered this stress for herself by conducting a switching spell that left her in tears.
While later in the manga, Yamato meets with Natsuo, Kouya does not come and all depictions of her after breaking off from nagisa are told from Yamato's point of view. Yamato was also the one to reach out to the Zero boys in the first place. It's unclear if Kouya wants anything to do with the fighting world anymore, and it's also not shown if she'd be friendly towards her successors.
- Kouya and Yamato are the only two lesbian characters in the Loveless series.
- Kouya along with Yamato are the first Zeros series, engineered by Nagisa.
- The Sagan brothers often refer to Kouya and Yamato as "Grandmas," despite the fact that they do not appear even remotely elderly. This is probably because they are the first Generation of Zeros. As a result, they view the first Generations as old since they are outdated.
- Kouya's Zero series is 'defective', given that Yamato developed the ability to feel pain.
- Nagisa planned to pair Kouya and Youji (her favorites) up and discard Yamato and Natsuo
- It's unclear whether or not Kouya also developed the ability to feel pain, or if it was only Yamato.
- Even though the English dub reverses the order of a character's name, Kouya's name is still referred to as "Sakagami Kouya" instead of the other way around.