In the anime, Imaizumi is given an original backstory. When he was younger, he had no social outlet in school, avoiding the other students, and seemed disinterested in everything. However, his butler, Takahashi, took him to Kanzaki Tooji's shop to look at potential bikes for his birthday. Imaizumi eyed the blue Scolt bike hanging on the wall, and Tooji noticed. Tooji gave him a smaller road bike to try out. Imaizumi ended up disappearing for two hours as he rode it around, which panicked Takahashi, but Tooji didn't mind. Imaizumi loved riding the bike so much that he bought it and entered his first race. Right away, the noise of the pack bothered him, so Imaizumi aggressively broke away from the pack to ride at the front where it was quieter, and won the race, much to everyone's surprise.
A New School
Imaizumi is introduced in Ride 1 when the car he is being driven in accidentally bumps into Onoda Sakamichi on the way to their first day at school. His startled driver, Takahashi, approaches Onoda and is further surprised that the boy appears to be unscathed and thinks nothing of the incident because he falls off his bike so often. They apologize to each other as Takashi is called back to the car by Imaizumi.
Being impatient and tired from morning practice, Imaizumi in disbelief when he hears that someone had been riding a city bike on a slope as steep as the back gate's, an incline greater than 20%, imagining they could only be pushing their limits. However, Onoda shows no signs of strain and is left smiling as Imaizumi leaves.
As another first-year student newly attending Sohoku, Imaizumi is seen preparing to go riding after classes. Although intending to join the school's cycling club, he has yet to turn in his application and greet the club's seniors, suspecting that ignorant first-years will soon drop out from the physical strain of practice. He's stopped by a female student from his middle school, who comments on his second-place finish at the finals. Imaizumi ignores her without comment but thinks there's no glory in finishing second. He vows to defeat Midousuji at the Inter High.
Imaizumi, ready to start practice, and Onoda, ready to go to Akihabara, unknowingly line up beside each other at the back gate on their bikes. A startled Imaizumi asks who Onoda is, and the boy introduces himself. Onoda's given name, Sakamichi, is unusual to Imaizumi because of it's connection to hills, but he dismisses Onoda's introduction and tells him (despite not being one to worry about others) that the back gate slope is too dangerous because while shorter than the main gate's route, the incline is much steeper, and if not able to break, a bike's speed can hit 80km per hour downhill. After hearing of the boy's intended destination, he reminds Onoda that the Sobu Train Line is closer if going through the main gate, to which Onoda replies that he's going the full trip to Akihabara by bike, but Imaizumi curtly takes off with a warning not to get in his way.
Thinking himself alone, Imaizumi is in disbelief yet again to hear that an otaku is going to Akihabara by bike, speaking aloud. Onoda suddenly appears behind him to continue their conversation. Imaizumi yells at him not to follow and that it's too dangerous to ride down the slope, but Onoda tries anyway and while explaining his reasons for riding, ends up falling off his bike. Imaizumi stops and runs to help Onoda, but the boy simply smiles up at him and says that he's going by bicycle because it's free: the money he saves from not using the bus nor train can be used for capsule toys instead. Imaizumi, dumbfounded, disregards Onoda entirely, thinking him an idiot for riding a 45km trip from the school to Akihabara, which takes an hour by car. Although he wonders about Takahashi telling him the student they hit that morning was riding up the slope like it was nothing, Onoda's sudden panic over his missing wallet leads Imaizumi to abandon Onoda there as just an airhead.
A short while later, Imaizumi is practicing by riding up the back gate's slope; he reflects on how riding uphill is about conserving power, reducing weight, and having rhythm, and thinks of his loss to Midousuji, who overtook him with a five minute lead while going uphill over three slopes. Calculating all the variables in his mind, he notes how the slope keeps getting steeper. To his surprise, he spies someone ahead of him, but is unable to determine if it's one of the seniors from the cycling club. Imaizumi considers himself better than when he lost, and decides to overtake the rider ahead of him as a test. As he approaches, Imaizumi hears them singing, and feels insulted, speeding up until he's beside them and notes how slow the rider is moving. At that moment, he realizes that the rider is in fact Onoda singing his favorite anime's theme song while climbing the slope on his city bike with ease to retrieve his wallet. Upon being caught singing, Onoda is startled and embarrassed. Imaizumi's chase leaves him baffled, and with a pulled muscle.
That night, Imaizumi trains vigorously on the rollers at his house, 20 sets of 60 second sprints, until he falls off his bike from exhaustion, driven purely by his desire to defeat Midousuji Akira. When he showers afterward, he thinks back on Onoda, and decides that whether the boy's abilities were a fluke or not, he refuses to lose to anyone, and will become the fastest person in the world.
Imaizumi searches for Onoda's bike after school the next day but can't find it. He wonders if it's been sent in for repairs. Eventually, he finds Onoda, shaken and yelling with frustration, inside the school after a physical education teacher tore up Onoda's anime club recruitment poster. Ignoring the boy's distraught state, Imaizumi claims they have a score to settle. He brings Onoda to the school's roof.
Onoda initially believes that Imaizumi wants to steal his anime merchandise, but in truth, Imaizumi challenges Onoda to a race. At first, Onoda doesn't understand nor accept the challenge, but finally does once Imaizumi says he'll join the anime club - but only if Onoda wins their race.
Imaizumi is shown to be serious about cycling, as he immediately plans to attend the Inter High. He also puts himself through intense daily training, revealing that he cycles 70 km, sometimes over 90 km (the distance of a return trip between high school and Akihabara, which was Onoda's weekly trip) every day. After meeting Onoda on the intense slope of the "back-gate hill" when they were both riding, he decides to challenge him to a race. Imaizumi is interested in Onoda's high cadence climbing style, and uses the race as a chance to test him. To his surprise, he ended up getting serious because Onoda actually caught up to him a few times, despite the self-imposed 15-minute handicap and tripping on the gutter, Imaizumi was still the victor. After the race, he let Onoda keep the cheap-model cycling computer.
Joining Sohoku's Cycling Team
After the Inter High
Onoda is assisted by Imaizumi and Naruko in explaining to his mother why he'd been racing at Mt. Fuji. She has no idea what they're talking about, so Naruko puts it simply that Onoda became the fastest person to climb Mt. Fuji and shows her a magazine article on him. After she laments how she didn't have a camera to take photos herself, they're all shocked to learn she was at the race. Before they leave the Onoda family's house, Onoda's mother tells them to be careful but keep working hard at cycling, and for Imaizumi and Naruko to take care of Onoda.
The first-years arrive to meet Sohoku's third-years on the road. Because he won the Inter High, Onoda leads the next practice, and takes the team to Akihabara. Imaizumi and Naruko can manage, but the third-years feel extremely out of place. Imaizumi witnesses as Onoda gives gifts to the third-years that they don't grasp. Onoda admits that they're all graduation as well as gratitude presents for the third-years for bringing him to the Inter High. Onoda thanks them all for their help in realizing his potential. Although previously confused at being in a strange place, the third-years accept the gifts.
While the team is distracted as Onoda explains things about Akihabara to Tadokoro, who mistook greeters for foreigners, and Onoda's questioning if the third-years will continue to attend practice, Imaizumi notices Makishima lagging behind; the team is unaware of Makishima's thoughts that despite his gratitude towards them, which can't be measured like Onoda's by the amount of gifts to one person, this is really farewell.
In the anime, Makishima's monologue is cut, as the team rides happily from Akihabara together, with Imaizumi and Naruko engaging in a race, knowing they will be the ones carrying the team along with Onoda.
The first-years all gain new equipment after the special trip to Akihabara, Imaizumi's being a new Scott frame with motorized gear shifters from the Kanzaki's shop.
After the Hakone Academy third-years have completed their day at a theme park, they look over the photos taken earlier and are startled to see Imaizumi and Onoda 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.