Arakita used to be a baseball pitcher with a bright future, but he was unable to continue down this path due to an elbow injury that occurred during the summer of his second year in middle school before he could make his debut at the prefectural tournament. After it healed, Arakita tried pitching again but was unable to throw as well as he used to. His fellow teammates mocked him for it. Feeling cynical, he decided to go to Hakone Academy, a high school without a baseball club. During his first year in high school, he was disappointed and angry at the world to the point of walking out of class and chasing off any friends (who he treated as lackeys). Even when he reached out to a cat whose freedom he admired, it ran away, worsening his loneliness. Searching for an outlet, Arakita ended up lashing out at Fukutomi when they happened to meet on the side of the road, insulting him and knocking over his bike, and even pushing him to the ground when Fukutomi claimed the point of riding his bicycle was that it moved him forward with certainty. Unfazed, Fukutomi challenged Arakita to a race in response: his bicycle against Arakita's moped. Arakita was confident that he would be the victor with his fast moped, but Fukutomi easily overtook Arakita and won, crushing what he thought was reality.
After Arakita's loss, he secretly tried (and failed) to ride Fukutomi's bike at night several times without the other boy's permission. The outcome of his race with Fukutomi frustrated him and he wanted to figure out why he lost. Fukutomi caught him in the act one night and told Arakita that he could only successfully ride if he looked forward and relinquished his past ties. Fukutomi told Arakita he could either return the bike or bring it with him and join the club. Frustrated, Arakita returned to his dorm room and cut all his hair. Other club members were worried that Arakita would just run off with the bike, but Fukutomi insisted that he would return with it. As predicted, Arakita did return, determined to become faster and climb to the top of the cycling world. Fukutomi told him that this "top" was the Inter High, so Arakita vowed to compete there, even after his upperclassmen laughed and told him it was impossible for him. Arakita told them that he'd flip their reality on its head, since he saw how reality could be changed himself.
Fukutomi introduced Arakita to the world of cycling, allowing him to join the team but limiting his participation to using the rollers for two hours each day on a heavier road bike borrowed from the club instead of racing. Arakita followed Fukutomi's instructions, but was still quite standoffish, making him unpopular with the other members, and he was quick to become physically violent, usually collapsing from exhaustion before managing to attack anyone. When Shinkai Hayato, prompted by Toudou Jinpachi's comment on how Arakita refused to talk about his past, asked why he rode a bike, Arakita angrily declared it was to prove that he existed as himself, to see how far he could go. Shinkai remarked that he understood why Arakita was brought into the club, that "Juichi likes the weird ones" with a strong will, which is needed to go faster. Arakita was left confused, not understanding how anyone could like him.
Eventually, he was able to compete in a race, completely bypassing practicing outdoors, although Fukutomi refused to tell him any details of how races worked. He only said that Arakita should come find him at the front if he had any questions. Enraged and filled with the desire to prove himself, Arakita accepted the challenge and passed the competing cyclists within four laps until he found Fukutomi. However, when Fukutomi asked him what question he had, he was unable to answer. Instead, Arakita immediately collapsed from exhaustion and dropped out of the race.
Afterward, with the Manazuru Circuit race coming up, Arakita was enraged when seniors of the club mocked Fukutomi for aiming only for second place and Fukutomi never retaliated. However, after Fukutomi revealed he would be the newcomer's assistant to push him into first place, Arakita became dead set on winning. He was given Fukutomi's bike to ride again for the race, and thereafter keep, and followed orders to stick behind Fukutomi until the last stretch, where he sprinted to first and won. After this rough start, Arakita became a skilled, though quite reckless, cyclist who works well with Fukutomi, acknowledging that he couldn't have moved forward without him and won that race. He changed his nickname for Fukutomi from "Iron Mask" to "Fuku-chan".
Building Hakone Academy's Cycling Team
Prior to the Inter High, Arakita is introduced as a Hakone Academy third year riding on the training rollers and complaining about the several interviews the team has been having to endure. He's present for an interview where several photos are taken of the team. When Manami Sangaku, a new first-year in the club, arrives late and misses the interview, Arakita scolds him for never intending to attend it. In the manga, he is the one who tells Manami to scout out Sohoku's training camp.
The anime adds a few extra, brief scenes beforehand: one where Arakita implies that Hakone Academy will win the Inter High no matter what, and a scene after practice where he wonders where Manami has disappeared off to on the day that Manami first meets Onoda Sakamichi.
F-Group Selection Race
He oversees the race between Manami, who he sees as the team's problem child, and Kuroda Yukinari, who he believes will win. After Kuroda loses, Arakita vouches for Fukutomi to still choose him over Manami as the sixth member of Hakone Academy's Inter High team, albeit to no avail.
On the first day of the Inter High, he works as an assist to Fukutomi. When Toudou becomes distraught over the fact that Makishima wouldn't accept his challenge, Arakita is the one to (mistakenly) point out that Sohoku only has one climber, and he reminds Toudou that his job is to take the mountain checkpoint. After Toudou leaves everyone behind to ride alone, Arakita is told by Makishima that Sohoku has a second climber who should arrive in three minutes. Arakita refuses to believe him; He insists that no proper cyclist in last place could pass 100 people nor the massive pack of riders clustered together behind them. Imaizumi calmly states that their second climber is never proper. Arakita is left in disbelief when Onoda does arrive.
After the mountain checkpoint, Arakita assists Fukutomi by bringing him to the finish line. The two battle against Sohoku's ace Kinjou Shingo and his assist Imaizumi Shunsuke starting 4km from the goal. At first, Fukutomi is riding in front of Arakita and allows the Sohoku members to gain distance, causing Arakita to complain, but Fukutomi wonders if the sight of them still ahead, 3km from the goal, doesn't excite Arakita. Spectators wonder about who will win the first day; one of them recounts that Arakita has been working with Fukutomi since fall of the previous year in several races, and that the two have won each race.
Toudou is seen talking to Makishima, describing Arakita as a "weird guy" who likes to take breaks and tends to be one of the slowest when practicing, but warns that in a major event like this, he's entirely different, with a determination like that of a wild animal. Toudou goes on to warn that if Sohoku is riding within Arakita by only a few dozen meters with 2km to the goal line, Hakone Academy will win. The aces and their assistants quickly pass both of them.
In response to Fukutomi's question, Arakita becomes all fired up and begins riding recklessly to the point of slamming his pedals into the road and knocking his body against the guardrail, parked vehicles, and almost the spectators he passes. He scoffs at the crowd cheering him on to "do his best"; in his mind, he's arrived at the Inter High by his own strength, so people just sitting on the sidelines have no right to tell him that. It's here that he admits that Fukutomi is the only one he acknowledges.
The two Hakone Academy members finally catch up to Kinjou and Imaizumi, the latter of which Arakita starts taunting and dismisses as a "good boy" as he doesn't think Imaizumi, while impressive to keep up with third-years, is strong enough, nor wild enough, to be riding at the goal zone. Arakita, "smelling" the goal, quickly passes him with Fukutomi in tow, and calls for Kinjou. But Imaizumi proves Arakita wrong by accepting his true nature and puts Arakita on edge, shouting for the Hakone Academy member to move out of the way and riding as aggressively as Arakita does to chase him. According to Arakita, Imaizumi's "scent" completely changes. The two have an intense race to launch their respective aces as Imaizumi tries to break past Arakita, ending up neck and neck with each other at the 500m launch mark. When Midousuji Akira surprises them by arriving next, Arakita is too exhausted to keep up and consequently is unable to stop him. After the results come in that Hakone Academy, Sohoku, and Kyoto Fushimi all tie for first, Arakita is seen at his team's hotel room that night complaining that he wanted to win by a large margin, to which Fukutomi assures him they can on the third day.
After the Inter High
Sometime during the colder months, Toudou suggests to Arakita and Shinkai that the Hakone Academy third-years should attend a special trip before they graduate. Arakita initially isn't interested, but Toudou convinces him when he says the trip will be to show their gratitude to Fukutomi as their captain. The three of them eventually decide on a theme park they find in a magazine, because one of its mascots, a lion, resembles Fukutomi.
When they arrive at the park, it appears more deserted and lackluster than the magazine portrayed; Arakita complains, and Toudou is worried that Fukutomi is disappointed, but Shinkai assures him that it's simply Fukutomi's default face.
Per Toudou's direction on the "guide rules" of enjoying a theme park, the third-years buy mascot hats from the gift shop, with Fukutomi immediately taking a liking to the lion's hat and Arakita grudgingly wearing animal ears of another mascot. They take several photographs together before hopping aboard a roller-coaster. Arakita acts like it's no big deal, but starts screaming as the ride takes off downhill, while Toudou laughs. While Shinkai and Toudou are unaffected by the roller-coaster, Arakita is shakily impressed, and Fukutomi is frozen stone-faced with fear.
Shinkai grills a meal for everyone afterward and strikes his "Bang!" pose; they take this as a challenge to eat everything he serves (although Arakita is mad he's only served meat). They accept the challenge and begin eating, but Shinkai serves faster than Toudou can chew, so he yells at him, which startles Shinkai so bad that he knocks over a drink onto the grill. The resulting steam burns Fukutomi's face.
In the swan boats at the theme park, Arakita and Fukutomi, in one boat together numbered "12", race Toudou and Shinkai, paired in another boat numbered "43", as if it were a race on the road. Toudou is able to use his "Sleeping Climb" technique to pass Fukutomi. Fukutomi orders Arakita to start pedaling, as like a road race, catching a glimpse of the enemy ahead drives Arakita to chase them down. However, Shinkai switches pedaling with Toudou and unleashes his "demon form" to battle it out with Arakita. In actuality, the boats barely move across the water, and seeing other park-goers watching them embarrasses them.
At the end of the day, the third-years ride the Ferris Wheel to see the illuminations (a light show). Arakita, Shinkai, and Toudou are worried the trip was a disaster that Fukutomi didn't enjoy. Fukutomi suddenly states he has something to tell them. Arakita immediately blames Toudou for the whole thing, which sparks an argument with Toudou that Shinkai can't quell. However, Fukutomi thanks them. To Shinkai, he tells him he did well overcoming his trauma to return as their ace sprinter, the fastest and strongest in history. To Toudou, Fukutomi says there is no better climber who climbs so beautifully and fast, and that the name "Mountain God" suits him perfectly. To Arakita, Fukutomi says his beast-like desire for the goal is admirable, and that he's done well carrying Fukutomi and the team with it. Fukutomi claims he's fulfilled his role as captain thanks to them. Arakita and the others are embarrassed, but as the fireworks and light show start, a message relayed to them from Fukutomi displays across one of the buildings, which they happily read aloud: "We are strong."
Afterward, they look over the photos taken earlier and are startled to see Onoda and Imaizumi racing on children's bikes in the background of one. Behind them, team Sohoku (minus Makishima) rides on a multi-person bike, with Kinjou running behind them, shouting about how Sohoku never gives up.
Year Two Events
After graduating, he began attending Yonan University, where he joined the bicycle club along with Sohoku's Kinjou, where they are also classmates in History of Modern Biology (a core paper in BSc (Biological Science majors)). Arakita appears eager to face his former teammates Fukutomi and Shinkai in an upcoming race.