Rei Serizawa/Relationships

Over the course of the series, Rei meets many people, from his allies and friends to rivals and enemies.

Aoi Haruno
Being both an cousin and an older brother to Aoi, Rei is particularly protective of her and even declares that he would save her how many times he needs to.

Masaomi Haruno
Despite being his biological uncle, Rei and Masaomi have a fairly complicated relationship. At first, Rei is shown to be fairly fearful of Masaomi considering his monstrous power. He believed Masaomi to be a threat that only Hisashi or even Eliza could handle. In Volume IX, they would come into direct conflict with each other as Masaomi began enacting his plan for revenge against the Vatican and as well as the rest of the Tatsuyama Village and the C.P.S.. While visiting the sight of the tragedy caused by Nosferatu, Rei is confronted and taunted by his estranged uncle. This in turn causes Rei to think about how Masaomi is able to see right through him. The idea of Masaomi being able to see through Rei becomes pivotal as Masaomi enacts his revenge plan and strings Rei along in order to manifest Kouryuu. Even after learning the truth about Masaomi as well as his father and Hisashi being attempted clones of the Storm God Susanoo from Kaoru Nonaka, Rei only hardened his resolve, since Masaomi became a direct obstacle to his and others' happiness.

Before beginning the battle to decide the fate of everything, Rei and Masaomi have a conversation. This is where Rei comes to the conclusion that Masaomi isn't necessarily wrong to hate the Vatican, but the two of them have a fundamental disagreement with regards to the Tatsuyama Village and the C.P.S., and how to go about "saving the world".

Yuki Nonaka
Rei's childhood friend who never gave up on him despite his exile from the Tatsuyama. After his intense duel against other Village members (Seito Toujou, Kurumi Nonaka, Takahito Hayase) she was seen leaving with them and not going to school for a week which made Rei really depressed but that changed when he saw her in his house cooking Beef Stew, and held her in his arms then declaring that she is the new house member in courtesy of Hisashi's help, indicating that she is one of Rei's very important peers.

Kurumi Nonaka
Yuki's younger sister and also Rei's childhood friend before his exile from the Village due to an incident. Prior to his childhood, both Rei and Kurumi were in good terms as she used to call him as her big brother. After his exile, however, Kurumi began to despise Rei because of what he supposedly did to the Tatsuyama Village and her sister. After her battle with Rei, she reverted back to her old self calling him her big brother like she uses to but also at the same time began to develop feelings for him especially after moving in with him.

Keisuke Fukuyama
Rei's classmate and friend.

Nanao Sasaki
When Rei first met Nanao she was timid and calm. However as a result Helblindi interfering in the sports festival of their freshman year, they discovered each other's true identities. After Christmas, they became aware of each other as man and woman. By the end of the third term of Rei's senior year, and thus high school years, and Nanao's freshmen year, they began doing lewd acts together.

Rikka Kaijura
At first, Rei sees Rikka as his responsible class representative. However upon getting to know her, he takes notice of her cute and clumsy mannerisms, and even finds them to be attractive. He's happy that she likes him, and the thought of having sex with her has crossed his mind multiple times. However fearing the he might lose control and potentially hurt her, due to her being human and not having resistance to the spiritual, he's decided it's better for him not to try and respond to her feelings for him for now.

The Elders
The Leaders of the Tatsuyama Village who banished Rei under the assumption he was the one who allowed Nosferatu into the Village. He is shown to know their true intentions when it came toward Aoi and their ideologies of "Protecting the Human World" going to whatever lengths to accomplish their goals. This soon grows into full distrust after being called back to the village due to their actions in the Underground and Rei's and Takashi's hosting of powerful Daemon Lords, after the way they questioned Aoi's desire to live in peace with bias, use Yuki and Kurumi as hostages, and hearing their connection with Masaomi and the Vatican.

Takehito Hayase
A member of the Tatsuyama Village and childhood friend of Rei. Takehito lost his mother when during Nosferatu's Invasion of the village, and ever since Rei was exiled their relationship hasn't been the same. 5 years later, Rei and Takehito are reunited, but Takehito still holds Rei responsible for the tragedy in the Village.

Garo Akabane/Vanagandr
Rei's classmate and also observer from the Poseidon Faction. After coming to blows over Aoi, Rei and Garo decide to form a mutual alliance that would benefit the both of them. Their alliance first bared its fruit at the conclusion of the Samyaza Arc, resulting in the "death" of Mio. Garo would play a pivotal role in Rei's assassination of Rudolph, thus freeing the Underground from the tyranny of the C.P.S., and setting the stage for peace negotiations between the Cocytus and Enosichton factions of the Underground. Through all that their mutual alliance would grow into a genuine friendship.

Reinart Vorster
One of the Underground's youngest Daemon Lords and one of Rei's formidable rivals. Due to Reinart's actions against Aoi, Rei also sees him as an enemy until the young Daemon Lord invited the Orcus Faction to settle their score via a seven-on-seven duel, where both warriors are. After the battle, Rei befriends with Reinart and them once as allies to fight against the corrupted ministers on the Daemon Lord's Court.