Kazuki has developed relationships throughout the entire series among the Occult Research Club, the other Factions, his own independent team even within those among the Khaos Brigade and the Vali Team.
Both Issei and Kazuki have a typical brotherly relationship for twins. Kazuki deeply cares about and respects his brother, despite the fact that everyone seeing him as only a pervert. He also never wanted him to be involved with the other side of the world. And despite finding out that they were holders of the Two Heavenly Dragons, they both still carried their normal relationship. They both started their own rivalry with each other, promising each other to fight one day to find out which one of them is the strongest. Kazuki always believes that Issei can grow stronger than he is now if he dedicated himself. It always amazed Kazuki how Issei surpassed him in strength with just his own strong feelings.
Kazuki shares a friendly relationship with Rias, as shown when they had shared a short dialogue with each other after he exited the Student Council Room. This was also shown when Kazuki hated the fact that she was in a forced engagement with Raiser Phenex and even assisted his older brother in saving her during the official engagement party. Rias has also shown concern for Kazuki's well-being after they had heard he was kidnapped by Alistair Eligos who was enraged after hearing what happened. And Kazuki has even admitted to Issei wanting to strengthen his relationship with Rias, because he wants to be a brother-in-law.
Both Kazuki and Akeno had originally shared more of a friendly relationship with each other, however after they continued to be around each other their relationship deepened. Kazuki has shown to care deeply about Akeno as shown when he was angered after seeing her and the other being beaten during their Rating Game against Raiser. Akeno has also shown that she would do anything to protect Kazuki as shown when she had used her Fallen Angel powers to save his life. Both of them have shown to be compassionate with each other and admits to loving one another.
From their interactions with each other, they have a friendly relationship with each other. Along with the fact that they are both hated by their fellow male classmates. This was even proven when he along with the rest of the Occult Research Club members went to rescue him from Alistair Eligos. And Kiba has deep trust in him to protect his younger twin sister, Yumi.
Kazuki originally met Koneko by chance when he was at his Second Year in Kuoh Academy, that she was attacked by a Fallen Angel. He immediately jumped in and rescued her, it was during that fight he first awakened his Divine Dividing to save her. After that day, Koneko started to see Kazuki as an older brother. And she started getting jealous as Millet started to hang around him when she started to see him as an older brother. After the Summer Break, she started calling him 'Onii-Sama'.
Despite their first encounter, when she had tried to attack him after thinking that he was trying to attack Yumi. Along with the fact that both are usually seen arguing with each other. Xenovia the started seeing him as a friend and a fellow ally, along with someone that she wants to have children with. As their relationship with each other started progressing they started having a mutual infatuation with each other.
Through their first encounter with each other, they had a friendly relationship. This was also shown when he saved her from Freed, the Fallen Angel and the rest of the Stray Exorcists. And Kazuki along with the other members of the Occult Research Club members was shocked and enraged by her "Death". He also endorses her increasing her relationship with his brother.
Kazuki has a friendly relationship with Gasper, with Gasper even seeing him as his Senpai and someone that he respects along with how he sees Issei. Gasper even declares that he wants to be as confident as both of them.
Both Kazuki and Irina are childhood friends and each other's crush. There wasn't a moment when they weren't with one another, whether it was playing, praying or just hanging out with each other. He was extremely saddened when she moved away from Kuoh Town and he was extremely ecstatic when they were reunited with each other. Kazuki has shown to be completely brutal and ruthless against anyone who dared harmed her as shown during his short fight against Kokabiel. During the aftermath, both of them had proclaimed that they had loved one another and kissed before parting ways again.
After transferring to Kuoh Academy, Kazuki started to have a more respectful feeling towards Sona. This is due to the fact that they are among the same intelligence, and are seen playing chess with each other. They then noticed that they starting have affections for each other. And they finally admitted to each other that they had feelings for each other after first meeting each other.
Though Saji was originally creeped out by the fact that Kazuki was a reborn Dragon, along with not liking him with the rest of the male students. But later on, Saji started seeing Kazuki as both a friend and rival along with how he sees Issei. He is also slightly jealous of the fact that Sona fell in love with Kazuki.
After their first meeting during her entering Kuoh Academy under her alias as Yuuma Amano, both of them entered a friendly relationship with each other. She then asked Kazuki on a date, near the end of it. She protected Kazuki has he was about to be blindsided by a Fallen Angel and was willing to die for him. After that, Kazuki started caring deeply about Raynare and would do anything to protect her. And Raynare loves Kazuki back, even getting jealous when other girls try to interact with him. He also trusts her to be the Vice-Leader of the Avalon Team when he's not around.
Despite her trying to kill him after their first encounter, he started to care about her like his little sister. And after saving her from her actual older brother, Kazuki adopted her as his little sister. Mittlet also looks up to Kazuki greatly and respects him as both a brotherly figure and as a leader of the Avalon Team, even calling him 'Onii-San'. She even entered a rivalry with Koneko for his brotherly attention.
Despite their first meeting, when she thought that he was Freed. Yumi actually started to have a deep admiration for Kazuki for being both strong and kind, which later turned into love. Her feelings were shown when she was angered by the fact that he was kidnapped by the Alistair during the night. Kazuki cares deeply about Yumi and he also showed to have some affection for her, as she was also one of his first choices for his team. Yumi also has the same level of affection for him and she respects him as their leader.
Despite their first odd meeting in Kyoto, Kazuki has shown to deeply care about her as a friend and ally. As they started hanging around each other, Konoka started to care about him as a friend and leader. And she even lectures him whenever he does something reckless. Kazuki is also wary because of her odd affection for things that she loves cute things, especially Youkai and keeps her away from Koneko.
After their first meeting after, he was attacked by the main members of the Hero Faction. Nagi has learned to trust Kazuki as a leader and as a friend. After their several battles with each other, Nagi feels like he can trust Kazuki in whatever situation that they get caught up in. Kazuki also trusts Nagi as someone who'll always have his back in whatever situation.
Sieghart has a friendly relationship with each other as shown through the battles that they fought together. And Sieghart acknowledges Kazuki as a leader and a worthy fighter. Kazuki also trusts Sieghart as his teammate, but he can get slightly annoyed with as shown when he attempts to get on Asuna's nerves. Sieghart has learned to trust Kazuki in any situation that they get caught up in.
Despite just meeting him, Kiyoko has shown to have a more 'direct' relationship with Kazuki despite only just meeting him. Kazuki sees Kiyoko has a Silver-Haired Xenovia, but he trusts her greatly. After he stopped her from going berserk, Kiyoko deeply trusts Kazuki more than anyone else and would follow any direction that he gives. Kiyoko later started seeing Kazuki and the rest of the members of Avalon, as the family that she had lost.
Despite their first meeting when Asuna tired to kill him. Kazuki deeply cares about Asuna's well being and is the one of the people trying to help her readjust to her new life. And Asuna as shown to deeply respect Kazuki as both her friend and leader. She also gets annoyed when he does something reckless and scolds him Along with Konoka.
As a strong believer and follower of the Church, Kazuki has an immense level of respect for Michael. And Michael acknowledges Kazuki as someone who's worthy to be a possessor of the Joker card bestowed upon him by his sister and even trusts him to protect her.
Kazuki has immense respect for Gabriel as both his King, Seraph and as a woman. He was greatful that Gabriel had acknowledged him as someone worthy of being reincarnated as her Joker, and he works to make sure that her trust wasn't wasted. Kazuki also sees her as an extremely beautiful woman that he has an attraction to.
Despite being a believer of the Church, Kazuki highly respects Sirzechs as a Maou who was given the title of Lucifer. Both seem to be on friendly terms with each other, through their usual interaction and conversations with each other about the future of the world.
Kazuki has shown to have great respect towards Grayfia, for both her strength and status as the "Strongest Queen" and the "Silver-Haired Queen of Annihilation". And Grayfia has shown to have great faith and trust in him, as shown when she left Lucina in his care. She even tries to help Lucina increase her relationship with Kazuki, and be more confident about her feelings.
Lucina has always had an attraction to Kazuki, ever since she saw him when they were both kids, but he never noticed her presence. When they first officially met each other, Kazuki immediately found her attractive. Through their several interactions after that moment, they both started having feelings for one another.
Both Azazel and Kazuki are on friendly terms with each other. They originally met each other, after he fought against a Fallen Angel to protect Koneko, he then explained his current status as the White Dragon Emperor. Their relationship remains the same despite him admitting to spying on both him and his brother since they were twelve.
Kazuki sees Vali as the rival that he wants to surpass, through training with each other Kazuki acknowledges Vali for his talent, strength and demonic powers. This drive to surpass Vali had increased after Kazuki was barely able to fight against him during the meeting of the Three Factions when he was barely able to put up a fight against him. Later on, Kazuki started to see Vali as both a friend and ally.
Their first meeting was when Kazuki found her in her in the form of a normal black cat. After finding out about her being a Youkai and Koneko's older sister, both of them started off on a friendly basis. Kazuki also wants both her and Koneko to rekindle their relationship. As their relationship progressed, Kazuki started having romantic feelings for her.
Kazuki has a lot of respect for Arthur as he was the one who had taught him "The Way of the Sword". Arthur also sees Kazuki as a worthy opponent as a swordsman. And he trusts him as a friend and ally, Arthur also trusts Kazuki look after his sister.
Kazuki greatly acknowledges Le Fay as a skilled and knowledgeable Magician, as she was the one who taught him all about Magic. He sees Le Fay has a great friend and would protect her from anything. Through their interactions with each other, Le Fay also seems to have developed a crush on him.
Through their first encounter with each, Kazuki has an immense hatred towards Bikou, because of his attitude and nature. And he never held back when both of them got into a fight, and he openly expressed the desire to want to hit him.
Kazuki immensely despises Creuserey from the very start for using Konoka as a tool for unsealing an Ancient Demon to try to kill Rias and Sona. And he shows no mercy against him when they fought against one another.
Like Issei, Kazuki immensely despises Shalba for causes of Asia's "death".
Through their first encounter, Kazuki immensely despises Cao Cao for brainwashing and using Leonardo as a fight in the Hero Faction. He also sees Cao Cao as a 'Villain' who are trying to pretend to be a Hero.
Albion is known as the White Dragon Emperor, sealed inside of Kazuki's Sacred Gear/Longinus. Kazuki has a deep respect towards Albion and acknowledges his strength and status as a Heavenly Dragon. Albion cares about Kazuki and was adamant of him learning about the Juggernaut Drive, after what happened to his past host. He also sees him as one of the only people who didn't see him as a tool to gain power and even sees his two past hosts in him. Like Ddraig he cares about Kazuki, despite the fact that he's the reason that he's the reason for his current title.
Kazuki first met Ophis when he was in middle school, after meeting her in front of a Candy Store he saw her as a cute yet odd girl. And after their reunion with each other, Kazuki has shown to have a slight infatuation with her. Being born from the infinite of nothingness, Ophis herself has stated that she doesn't completely know her feelings for Kazuki, she just knows that she doesn't like seeing him hurt or sad. This was shown when she was adamant about him unknowingly wanting to join the Khaos Brigade and when she told him not to give into the Juggernaut Drive.
Through their first meeting, Tiamat has been flirtatious towards him, he's also the first person that she's ever formed a contract with. And their relationship only grew through training him over the Summer Break. She sees a lot of talent and possibly in Kazuki's future and believes that he'll eventually be at the same level as the Heavenly Dragons one day.
Though only having a short interaction with Tannin, Kazuki highly acknowledges Tannin as a powerful warrior and ally.
Past Possessor of Divine DividingEdit
Through their first encounter, Lancelot attacked Kazuki because he was under the influence of using Juggernaut Drive before he died. After Kazuki saved him from the negative influence, Kazuki showed that he had great admiration for his accomplishments as his own abilities and creating his own Sub-Species Balance Breaker. Sir Lancelot is also completely proud of his fellow possessor enough to give him advice in forming his own team.