Family
Valerie
Arlo's hero. Let that sink in.
Arlo's aunt was a member of the Authorities, and major influence in shaping Arlo's perception of them. When Arlo was little, Valerie presented herself as a sort of champion who always stopped the bad guys. Arlo trusted her, and the Authorities by extension. When several major incidents occurred during his high school years, Arlo thought it best for the Authorities to handle them. He was surprised to hear acquaintances such as Seraphina and Remi did not share his faith in them, pointing out that their progress seemed deliberately slow. Arlo had a hard time denying their arguments, so he reached out to his aunt in the hopes of getting some answers. Valerie told him she had transferred to Wellston Town recently, a coincidence that alarmed Arlo.
When Remi tells Arlo that Valerie is the one who killed Rei, he immediately dismisses her, unable to believe that his Aunt is capable of such a thing, and tells Remi to grow up and accept that Rei is gone. However, after an ordeal with Seraphina refusing the authorities offer to work for them and escape, Valerie starts to show her true colors and, remembering what Remi said, Arlo starts to suspect his aunt was the one who killed Rei.
Eventually, Arlo realized his aunt is not who he thinks she is, causing him to suffer mini breakdown.
Wellston Private High School
Rei
Oh he just can't wait to be King.
When Arlo was Wellston's Jack, Rei was his King. Arlo had always thought Rei's philosophy of using their powers to help those weaker than them was idiotic. While he disagreed with Rei's methods of running the school, Arlo actually admired his predecessor for recognizing talent, incredible strength, and charismatic way of getting along with others. Arlo took the news of Rei's death very poorly, unable to accept that anybody could kill him and angry that he would never get a chance at besting him in a fight. While this could have merely been anger after for never winning a battle, it could have also been a way of letting out his grief. In psychology, many people who are going through a loss will find something about the person they can never get back. In Arlo's case it was besting Rei in combat. When Cecile insulted Rei, Arlo immediately got aggressive and silenced her with a noticeable glare, showing how much respect he garners for his predecessor.
Kuyo
The man behind the nickname
Like Rei, Kuyo was Arlo's senior during his first year at Wellston. Though they weren't shown to interact much, Kuyo was seemingly fond of his junior. So much so, to the point of coining him the nickname Asslo. He also tends to playfully roughhouse Arlo whenever the opportunity arises.
Remi
If you didn't know Arlo was tall..Here you go.
Although they are both on Wellston's Turf Wars roster, they do not see eye-to-eye on many issues and frequently fight. However, they do seem to care about one another, however much they fight. The two are close enough to be on a nickname basis as Arlo gave Remi the nickname "Pinky," much to her chagrin, and in return, Remi calls Arlo by his nickname "Asslo." When attacked by 'Joker', Arlo becomes angry and intervenes the two's fight. He also becomes very angry at her violent defeat, stopping Joker from harming her more. It is around Remi that Arlo's more caring and protective nature emerge.
Remi's newfound obsession with EMBER was a major source of friction between the two. Though Arlo was as angry at EMBER as she is for killing Rei, Arlo believed she should stop risking her life chasing them and leave the matter to the authorities. Remi, having developed nothing but contempt for the authorities, outright refused Arlo's orders and left him frustrated about yet another high-tier who wouldn't conform to his ideal orderly world. This all changed when Arlo found out about EMBER's connection to the authorities, and while he still beseeched Remi to stay away from vigilantism, he stopped seeing the authorities as guardians of order. This was further fueled when he saw his Aunt Valerie's true colors at a café after a failed attempt to capture Seraphina, and after Remi told him that Valerie is a part of Ember and that she was the one who killed Rei.
In spite of this, Arlo and Remi care for each other, and worry about each other's injuries and problems.
Seraphina
Former king and queen
Despite Arlo and Seraphina being members of Wellston's current Turf Wars roster, the two did not get along at all. According to Remi, he and Seraphina always had "beef" with each other. According to Seraphina, their relationship soured on the day she made Blyke the Jack of Wellston, a choice that Arlo disagreed with. He now publicly treats Seraphina as a cripple, due to her losing her ability. However, did not have turned his back on her completely, as he told Elaine he still considered Seraphina as "one of us." Arlo also feels guilty as he had schemed and planned in order to drag Seraphina back into the hierarchy, now fully aware he went too far. More recently, he worked closely with Isen and her to uncover more information about Terrence, and the drug disablers. He also became very protective of her after her fight with John. He accompanied her to meet Leilah, inspite of Elaine's protests.
Holden
Holden, the most important character in UnOrdinary.
Holden appears to be Arlo's best friend. Despite not being a Royal, he is often seen walking alongside the King even when school isn't in session. Though at first glance, Holden appears to be a mere lackey of Arlo's, threatening students for any perceived offenses. Their bond runs deeper than this, and Holden's proven himself a legitimate friend who respects Arlo for more than just his power (unlike most students). He has shown concern for the King on numerous occasions, and trusts his leadership despite any rumours that may circulate about his capability. In turn, Arlo allows Holden to speak his mind without repercussions. He's even protected Holden without his knowledge by preventing him from provoking the most dangerous student in school.
Elaine
Arlo and Elaine
Arlo and Elaine are part Wellston's Turf Wars. Elaine is very loyal to Arlo and listens to everything he says. He also assigned her to keep an eye on Seraphina. Currently, both of them are aware and fearful of John's ability. Elaine also turns to Arlo whenever there's a crisis that she can't handle on her own, such as Remi's near death in her pursuit of EMBER.
Arlo is willing to listen to the concerns Elaine has, and seems to become less cold around her, if only a little bit. Elaine seems to have a crush on Arlo, which is not reciprocated, as he did not reply to her text saying "would you like some oranges?"
Arlo and Blyke
Blyke
During their first encounter, Blyke disrespected Arlo, forcing the King to put Blyke in his place. After Cecile was dethroned by Remi, Seraphina had appointed Blyke as the new Jack as opposed to the more powerful Cecile, which soured the relationship between the Ace and King. Despite this, Arlo does not appear to harbour any ill-will against Blyke and allowed him to keep his position as Jack. Blyke and Arlo share a cordial relationship on the whole. Further, he supported Blyke's ascension to King when John resigned.
Isen
A pictorial representation of Arlo and Isen's relationship
Arlo is Isen's highest-ranking superior and was the one who assigned him to find information on John. Isen is loathe to put his investigative skills to work for Arlo's whims, which happens quite often. He considers Arlo's obsession with order and the hierarchy to be "BS," especially following his disastrous attempt to bring John to heel. Isen also feels that Arlo's decision to make him head of the Wellston Weekly team to be one of many instances where he expects others to perfectly perform duties they're not qualified for.
However, Isen is nowhere near brave enough to say all of this to Arlo's face, unless he is too stressed out to think clearly. Usually, Isen only voices these hang ups when he talks in his sleep. A greater fear of John also keeps Isen from telling Arlo the whole truth until there's absolutely no other recourse.
For all of Isen's issues with Arlo, he still considers the King to be the best candidate to fix major problems in school. When Arlo had resigned to surrender to John's superior strength, Isen urged him not to give control over to someone so unstable.
Ventus and Meili
Arlo giving orders to Ventus and Meili
Arlo often relies on them as enforcers to beat up people who disobey him. Both Ventus and Meili are very loyal to Arlo, and follow his orders unquestionably.
Arlo also cares for them somewhat, as he asks Elaine to heal them before himself, right after their cataclysmic battle with John.
Cecile
Cecile vs Arlo
Cecile and Arlo were once old teammates back when Rei was King. However, their current relationship can be described as "shaky." Cecile detests Arlo for favoring Remi, and Arlo bears some ill-will against Cecile for insulting Rei and supporting articles that could potentially ruin his reign. Despite the mutual resentment, Cecile begrudgingly obeys her King's orders, and Arlo has shown her leniency due to her history with him. After learning about Arlo's defeat at the hand of John, Cecile wishes to make John the next King and spread the truth about the "Shadow King," all while dethroning Arlo in the process. When Cecile was ultimately fired from her position, she attacked Arlo, showing that she had lost most, if not all, of her respect for her King.
After John's ascension to King, Arlo advises John against relying on Cecile because of her capricious nature, further souring his relationship with her.
John
Arlo versus John
Arlo absolutely despises John for refusing to conform to his place in society as well as being the reason for Seraphina's change in behavior. However, at the same time, Arlo is intrigued by John, and correctly surmised that he's not who he pretends to be in public. He goes so far as to try and force John into the school's hierarchy by separating him from Seraphina and leaving him to suffer at the hands of the student body. As noted by Elaine, Arlo harbors a fear of John's power after their fight, but believes that his throne is not in jeopardy as long as John remains believed to be a cripple. That said, he takes care not to activate his Barrier near John unless they're in a public place, which ensures they remain on equal footing.
After Seraphina's ability loss, Arlo's disdain for John intensifies when he refuses to use his superior power to protect her. John often tries to order and intimidate Arlo in private, but Arlo is far too proud to obey a King who won't go public with his true power, even when the two of them have common goals.
Once Arlo realizes his faults, he harbors a sense of guilt towards John for pushing him and ignoring his and Seraphina's desires. Nonetheless, he still condemns John's running of Wellston as King, and his brutal treatment of the students. After John resigns, Arlo notices positive changes in his behavior, that prompted him to share Seraphina's Spectre story with John. They now work with Seraphina to ensure Spectre doesn't harm Wellston.
Zeke
Arlo did not seem to hold Zeke in high regards, due to the latter's personality. Likewise, Zeke only respects Arlo out of fear, and Arlo being stronger than him.
Others
Kassandra
Kassandra is Arlo's direct superior at the Bureau; both of them work under Valerie's supervision. He would later learn she is Rei and Kuyo's senior at Wellston. They shared one thing in common: being a fan of Rei. Arlo doesn't understand why Kassandra was so hellbent on pinning her junior's death on Vaughn, even though he agreed with her that the headmaster was far from innocent.
Together, they uncovered the connection between EMBER and the Authorities.