Tadashi Kikuchi[]
Ainosuke and Tadashi
Tadashi is Ainosuke's secretary. Although Tadashi treats him formally, Ainosuke sometimes calls him a "dog" when he's angry and a "good boy" when Tadashi fulfills his wishes. Tadashi obeys any order Ainosuke gives him even if Tadashi initially shows some concern about doing so, he will still obey even if it's to sacrifice himself to save Ainosuke from being accused of perjury for his corrupt political dealings. He prepares whatever Ainosuke asks for, which was revealed in the spinoff manga when he bought a flower bouquet that Ainosuke asked to give to Langa Hasegawa. Tadashi monitors and assists Ainosuke in "S", watching him through cameras, picking him up in a car before the police arrive and piloting a helicopter for him.
Tadashi and Ainosuke as children
As a child of a Shindo family servant, Tadashi has been serving Ainosuke since youth and he is the one who introduced him to and taught him how to skateboard as seen in a flashback with a young Ainosuke who has tears in his eyes because of the strict discipline from his aunts. Ainosuke is very important to Tadashi, but Ainosuke feels differently about him. Even in the past, Tadashi never crossed over the line of his position. Tadashi used to be a very important person to Ainosuke, but Tadashi didn't realize that. Since Ainosuke was born into special circumstances, Tadashi couldn’t even imagine that possibility before their friendship broke. Tadashi was a friend to Ainosuke until he did nothing as Aiichiro Shindo (Ainosuke's father) burned his board and banned him from skating. Ainosuke is furious when Tadashi, with the stated goal of making Ainosuke renounce skating, enters the tournament as "Snake," but begrudgingly allows it in the end, daring him to go ahead and try and win. After the confrontation, Tadashi is seen practicing skateboarding after looking at a pair of hearts engraved at the bottom of a skating bowl. Tadashi blames himself for how Ainosuke changed into a more cruel person as an adult and regrets teaching Ainosuke how to skate as that hobby could not be shared with another child of Ainosuke's social standing, further isolating Ainosuke.
Ainosuke and Tadashi meet up after the final race.
Tadashi changed his mind about taking skating away from Ainosuke after several conversations with Reki Kyan about how skating should be fun and forfeited his race against Langa in the hopes that Langa could teach Ainosuke to enjoy skating again. During Ainosuke's final race with Langa, Ainosuke recalled how skating with Tadashi during their youths was fun and seems to have let go of his former grudge against Tadashi. Ainosuke did not push Tadashi into taking the heat from the perjury charges for him, and instead claimed, with a smile, that Tadashi would be his dog for the rest of their lives. It seems as if the sour relationship he had with Ainosuke for so many years has changed after the tournament. After this, Tadashi probably will never leave Ainosuke's side and they will begin the process of reconciliation and healing to untangle the knots from their relationship, although it will remain as master and servant. It was also revealed that Ainosuke was the one who leaked Representative Takano's corrupt dealings and the entire scandal went according to Ainosuke's plan.
Langa Hasegawa[]
Ainosuke and Langa
Ainosuke is very interested and fixated on Langa that he starts to show himself in "S" after a long absence because of Langa's unique skating style, even giving him a bouquet of roses before they compete. It is not clear what kind of attraction Ainosuke shows to Langa, but he does imply it as a "passionate love". Even as soon as his Love Hug technique was dodged by Langa, he began to call Langa as his true "Eve" and thinks Langa is the same type of person he is. Ainosuke sets up a tournament at "S" to be able to race against Langa again. He was disappointed when Langa's first challenger in the tournament turned out to be Joe, although he was thrilled that Langa won his first race and publicly called Langa the name "Eve." He reviews footage of Langa and sees how he looks depressed, spiking his curiosity and later leading to spying on Langa and Reki Kyan's reunion using a drone. Ainosuke comments that he does not appreciate Langa enjoying skating with someone other than him. After Ainosuke's race with Reki and Tadashi Kikuchi's forfeit, Ainosuke is left standing alone and unhinged, declaring that Langa would take the role of "Eve" and fall with him.
Before his beef with Ainosuke, Langa muses about why Ainosuke is skating, now able to see himself in Ainosuke and empathize with him after having skated without having fun during his separation from Reki.
In the final episode where he races against Langa for the last time, Ainosuke seems oddly calm throughout the race (similar to how he acted during his race with Cherry Blossom). This is likely due to the fact that he had just been beaten by Reki in his last beef, he was technically abandoned by Tadashi and he now seeks to bring Langa down with him in their beef.
Langa asks Adam to skate with him
During their race, both Ainosuke and Langa entered the zone until Langa realizes he wasn't feeling anything at all and pulled himself out of it. When Ainosuke notices Langa isn't behind him anymore, he mourns that he's truly alone until Langa grabs his arm and pulls him out of the zone and back into the race. Langa declares that he is going to teach Ainosuke that skating with friends is fun, something that Ainosuke rejects and claims he doesn't need. Langa points out that if Adam truly felt that way, he wouldn't have tried to make Langa go with him. They clash together and they both collapse on the ground where Langa gets up first and picks up Ainosuke's board before holding it out to him and asking him to skate together. Ainosuke and Langa resume the race, skating side by side, and although Ainosuke is resistant at first, he recalls the feeling of how fun it was to skate with Tadashi in his youth, finally accepting what Langa is trying to teach him. Langa wins the race and Ainosuke leaves with Tadashi without causing a scene. Later, Ainosuke arrives at Langa's victory party by parachuting out of his helicopter with roses, crashing into everyone when he lands.
In the English dub, Adam gives Langa all sorts of cute pet names like "little Langa", "snowbunny/snowball", "icy spicy", "love" and "my little penguin".
Reki Kyan[]
Ainosuke and Reki
Ainosuke doesn't see Reki as anything special other than a stepping stone to crush to be able to race against Langa Hasegawa where he showed no remorse about crushing Reki's spirit and causing his injury. He was surprised to see Reki getting his spunk back, but not for long after putting him into a 'Love Hug' sending the youngster to the hospital. Ainosuke is seen grinning and licking Reki's blood off his face, calling the boy nothing but an appetizer.
Reki dodges Adam's Full Swing Kiss
He seems to have forgotten who Reki even was until he spies on Reki and Langa skating together and reaffirming their friendship that he sets his sights on Reki since the boy is taking Langa's attention away from skating with him. Ainosuke invites Reki to take Shadow's spot in the tournament and engages in a brutal race with the boy, physically assaulting him, while Reki refuses to back down. Reki's lucky break with rain, and having prepared for it with special wheels on his skateboard, lets him pull ahead and leads to Ainosuke slipping in the mud and having an emotional breakdown at being humiliated. Ainosuke is barely able to catch up and snag the win from Reki before he is left baffled when the crowd continues to cheer for Reki for putting up such a good fight even if he lost. Reki tells Ainosuke that he should never be in the position where he ends up by himself and Ainosuke admits that he is alone, but soon won't be, implying Langa would join him.
Miya Chinen[]
Ainosuke and Miya
Ainosuke had an interest in Miya due to the boy's skills at skating and hoped to cultivate those skills, giving him coaching and tips from afar. However, once Langa Hasegawa appeared at "S", Ainosuke uses Miya to lure him back when he doesn't make a reappearance for two weeks. Once Miya ends up losing his beef against Langa, Ainosuke is quick to dish out sniping remarks on why Miya is always left alone and pretty much points out how disposable he was. Miya is visibly trembling at these words and Ainosuke then shifts his full attention to Langa.
Ainosuke and Miya finally skated together for the first time during the tournament qualifiers. Miya was dismayed to see that Ainosuke was so far ahead of him and Ainosuke does admit that once Miya gets older he'd "love him" the same as all of his other skating partners he takes an interest in. Later during Reki Kyan's race with Ainosuke, Miya expressed horror at the injuries Reki was enduring.
Kaoru Sakurayashiki[]
Ainosuke and Kaoru
It was hinted in Episode 5 that Kaoru and Ainosuke were friends in the past along with Kojiro Nanjo, although he says that Ainosuke parted away from them first. It's been confirmed that Kaoru, Kojiro and Ainosuke were close friends when they were young, but Ainosuke had a falling out with the other two when he began skating in a ruthless manner in search of an "Eve" after feeling betrayed by Tadashi Kikuchi with Joe and Cherry personally witnessing a young man getting injured during a high speed race with Ainosuke. At some point, Ainosuke had to stop skating with them and leave for America.
Cherry wants to face Ainosuke in the tournament to settle a 7 year grudge, regarding Ainosuke starting his dangerous skating and to determine what was really in Ainosuke's heart. Cherry's only race in the tournament was against Ainosuke and he kept up pace with him, even overtaking him at times, right until the end when Ainosuke pulled ahead and then turned around to smack Cherry in the head with his skateboard. Ainosuke told Cherry that the reason he had rejected his challenges in the past was because he found Cherry's style of skating to be boring and predictable because of his use of AI calculations. This would explain why Ainosuke was uncharacteristically calm and quiet during his race with Cherry because he finds him boring.
During Reki Kyan's race with Ainosuke, Kaoru laughs when Ainosuke slips in the mud and loses ground to Reki.
During Ainosuke's final beef with Langa Hasegawa, Kaoru made goading remarks about Ainosuke in a fairly good-natured manner as the two raced neck and neck towards the finish.
Kojiro Nanjo[]
The trio as teenagers
It was hinted in Episode 5 that Kojiro and Ainosuke were friends in the past along with Kaoru Sakurayashiki. It's been confirmed that Kaoru, Kojiro and Ainosuke were close friends when they were young, but Ainosuke had a falling out with the other two when he began skating in a ruthless manner in search of an "Eve" after feeling betrayed by Tadashi Kikuchi with Joe and Cherry personally witnessing a young man get injured during a high speed race with Ainosuke. At some point, Ainosuke had to stop skating with them and leave for America. Joe wants to face Ainosuke in the tournament to punch him in the face, figuratively and probably literally, although he would not get the chance to race Ainosuke after losing to Langa Hasegawa. After the qualifiers, Joe spoke to Kaoru in his diner that he thinks Ainosuke is totally isolated and alone, a point he repeated again to Kaoru when the other snuck out of the hospital to visit Joe, and added on that he doesn't think Ainosuke is happy right now.
During Reki Kyan's race with Ainosuke, Kojiro joins in with Kaoru in laughing at Ainosuke's misfortune at losing ground to Reki and tripping in the mud. After Reki loses, Kojiro steps in front of Ainosuke when Ainosuke is approaching Reki and states that the beef is over.
During Ainosuke's final beef with Langa, Kojiro cheered on Ainosuke to be taken down by Langa.