When Nex first met Serin he was a human teenager going by his original name Jae-Hyuk Chae. Due to circumstances beyond their control, Serin accidentally strikes Jae-Hyuk down during a battle, seeing his desire to live Serin transforms him into an undead. After reviving him, Serin becomes his master and takes him away to her world, Chaos. The two develop a rocky relationship. At first, Jae-Hyuk is wary of her, but after numerous trials begins to see her in a more positive light. After Jae-Hyuk learns of Serin bringing his brother, Jae-Hoon, into Chaos and being transformed into the vessel of Caladborg; he tells her he longer wishes to see her.
Twenty years later, Jae-Hyuk has been given the title of Regis and now goes by Nexus Nex. Nex is married to a woman named Iffrita and has two children, Ninurrta and Miya. Nex holds no affection for Iffrita and Ninurrta due to suspicions. Soon the reader learns Nex has imprisoned a catatonic Serin deep within a sealed vault underneath the castle. After being injured in battle, Nex savagely draws blood from Serin and tells her she will belong to him for as long as she lives. When the current generation searches for answers to the past, Osky provides a flashback to what events transpire after Jae-Hoon is taken away to Earth. Jae-Hyuk and Serin have stopped all communication for the past two years and he shows great disdain whenever her name is mentioned. When Calaborg makes his return to Chaos and attacks Serin in the process, Jae-Hyuk learns about his return and rushes to find him. He finds Caladborg and his accomplice Nirvana torturing Serin. Jae-Hyuk and Serin join forces to fight off Calaborg. After Caladborg flees, Serin is brought to her house for treatment, Jae-Hyuk visits her and the atmosphere proves awkward.
Neither teenager can figure out what to say to the other until Serin breaks down crying. She confesses how sorry she is for all the events that had happened to him. He forgives her and the two share an intimate kiss. Once she recovers they visit a village, where Calaborg reappears attacking Chao's citizens. He tells his victims the attacks will end with Serin's death; Jae-Hyuk and Serin flee to regroup with fellow allies. The group head to Calaborg's location where the prophet tells Jae-Hyuk that it is inadvoidable that Serin will die. During a battle with Calaborg, the demon gives Jae-Hyuk two choices: save a possessed Serin or Chaos. Jae-Hyuk chooses Serin. The group decide for Jae-Hyuk to become the Regis to restore balance and during the ceremony Serin gives him the demon name, Nexus Nex. Nex and Serin make a final effort to save Chaos that almost causes Serin to die. She is revived and Nex is shown crying, during his coronation it is revealed Serin is his fiance.
Unknown events caused a pregnant Serin to attack Nex and flee which leads to the events in current times.
Iffrita became obsessed with Nex after their first meeting and does everything possible to gain his attention. She becomes more openly sexual because of her attraction and her father influencing her to seduce Nex. Iffrita was a very kind person but became cruel from jealousy and wishing to avenge her mother's death caused by Navarus. After remembering Navarus killing her mother she chooses to try becoming queen as a form of payback. She sleeps with her cousin, Mikhail, to tale advantage of his affections in order to gain his help for becoming queen. She becomes pregnant, but it's uncertain if Mikhail is truly the father since she approaches Nex and claims he is the father. After Serin flees, Nex makes her his new fiance but harbors no love towards her. Iffrita tries her hardest to gain his affection but it's all in vain since it becomes more and more obvious that Nex still loves Serin despite her betrayal.
Twenty years later, she is troubled that she may lose her position as queen and her son, Ninurrta, may get dethroned as prince. She is manipulative and cruel towards her servants and uses her power to try staying queen. After Just and Xix appear, she becomes greatly concerned and tries persuading Nex that both boys are fakes. She is infuriated after learning Nex has disqualified Ninurrta after his kidnap despite her efforts in lying.
When learned the truth about Ninoorut being Serin's son, along with the fact that she broke Depore, Nex completely showed no sadness towards Iffrita's death and instead showed great remorse for how she kidnapped Serin's son and framed Serin for her crimes, showing that he has no affection for his queen due to her twisted schemes for gaining power.
Nex pays little attention to Ninurrta who tries his hardest to gain Nex's approval. Nex has his doubts that Ninurrta is his son and when Just appears his doubts increase. Nex demands a ceremony preformed to prove which candidate is truly his son. Ninurrta is kidnapped before his turn. Nex orders his capture either dead or alive, Ninurrta finally decides to abandon his title as crowned prince after learning this.
It is later revealed that Nex had loved Ninoorut all always and never cared whether he was his son or not. He had pushed him away so that he would become a different Regis than he was showing that he cared nothing for blood ties.
Miya is Nex and Iffrita's daughter. Between Ninurrta and Miya, he shows more concern to the latter. Miya often questions if Nex loves her and her concern is lessen after learning Nex provides his blood to heal her. Miya suffers conditions similar to her uncle, Jae-Hoon.
Xix becomes a candidate for the true son ceremony when his blood releases an Imperial seal. Xix hates Nex for slaughtering his village and his closest friend, Siana, as a child. Xix swears revenge, but is never able to defeat Nex. Nex is interested in Xix, who he questions if he is his son. After Xix releases the seal, Nex keeps the boy close to watch his actions which infuriate Xix. Some of the other characters note that Nex's actions towards Xix begin to tone down after he questions whether the boy is his son; however, Nex is not above using pain to get Xix to bend to his will. If the two are related this could be an example of "tough love." During most of their interaction scenes, Xix glowers and spits out various insults at Nex which Nex, for the most part, either ignores or finds some amusement in the teenager's antics. However, their scenes together seem to always end with Nex either reprimanding the boy or nearly killing him.
In Osky's home Nex and Xix have finally amended their relationship with the two joining forces to stop Caladbolg once and for all in the Second Magnanix.
Nex's daughter confirmed as of later chapters, the two have not had any interaction with each other, but have run into each other on certain occasions. Nex actually met a young Siana once, but was unaware of their relations, but she did seem to catch his interest. Siana does share her father's traits in his youth, she possesses his stubborn and reckless nature and some of his goofy humor pre-Jae-Hoon possession by Caladborg.
In a sad turn of events, Nex is still unaware that he is the cause for Siana's early death, along with Xix's.
During a flashback scene he discusses with his then wife, Serin, on naming their baby "Siana" if it's a girl. Based on raws, Nex was excited on the prospect of having children with Serin; however, in current times Nex still has yet to actually meet Siana and shows no recognition of her name when Xix repeatedly demands to know why Nex allowed his warriors to slaughter their village.
Owen is Nex's best friend and one of the few allies that remained loyal him to him. Despite Nex's drastic personality change along with his cold indifference to Owen, it is clear that the two are still close friends. Owen has even punched Nex once with Nex showing little to no anger as he understood that it was only out of concern for him.
Depore is Nex's most trusted and loyal companion. Nex considers her the one person he can place his absolute trust in showing nothing but love and care towards her. Depore is one of the few people that know that Nex is actually a very kind man who has spent most of his life suffering in torment. In fact Nex and Depore show such a close relationship that when Depore was broken by Iffrita who was disguised at Serin, Nex completely lost any trust in Serin and was absolutely enraged to the point that he accepted Serin's treason despite spending an entire week not sleeping believing in Serin showing just how much Nex cherish's her.
Nex deeply loathes Caladbolg for his actions of causing terror and fear throughout Chaos. His desire to kill him is to the point of scaring Xix, Yuan, Owen, Just, and Biryunna all at once with all of them shuddering in terror of his rage.