As a child, Manami was very sickly and spent most of his time at home in bed playing video games. He bonded with his neighbor, Miyahara, whose bedroom window was right across from his. One day, when talking to her through the window, Manami wondered out loud what being stabbed felt like, since he didn't feel alive at all, unable to enjoy life due to his sickness and never feeling any struggle or pain sitting at home playing video games. Miyahara, pitying him, took him out cycling. Even though Manami struggled and fell due to his weak state, he enjoyed the feeling of pushing his body physically, feeling alive for the first time. As he grew older, his health recovered, and he was able to cycle more easily and grew to love climbing slopes.
Manami asked Miyahara to assist him in studying for the exam to attend Hakone Academy, where Miyahara was intending to go, in order to join the cycling club there. He and Miyahara attend Hakone Academy together, with Miyahara becoming his class's representative.
Building Hakone Academy's Cycling Team
Manami's love of slopes is apparent from his very first appearance, in which he takes a detour from school because he wants to bike up a hill. He passes a parched Onoda Sakamichi on the way, stopping to give him some water. He concludes that Onoda is a cyclist based on how he drinks from the water bottle Manami gives him. Manami tells Onoda that he loves slopes, and that can keep the bottle, saying that it is his duty to help people on the mountains he loves so much.
When Manami returns to Hakone Academy, his teammates scold him for not coming to the magazine interview. Initially feigning forgetting about it, Manami simply apologizes and states that he isn't interested in such things. He tries to leave, but is stopped by Toudou Jinpachi (although it was Arakita in the manga), who tells him that Sohoku is having a training camp nearby and that an interesting climber is there that Manami should see while scouting out the rival team. Manami smiles upon hearing this.
Upon arriving at the camp during the third day of Sohoku's training, Onoda, up earlier than the others, finds Manami riding on the track. Manami wastes no time in blatantly telling him that he's been sent to scout out the team but decided to ride because it was more fun. Though he told Onoda he was from Hakone Academy during their first meeting, Manami reveals that he's a first-year student and indeed a member of his school's cycling club, wearing their jersey under his shirt. He asks if Onoda will be participating at the Inter-High, and upon hearing that the boy isn't, exclaims how boring that is because he wanted to go to the Inter-High with Onoda, who loves slopes like him.
Onoda, embarrassed, tries to change the subject by asking for a race up the hill. Manami is instantly pumped up to go but Onoda remembers to thank him for his bottle and says he'll return it later. Manami replies that Onoda can have it - unless Manami wins this race, in which case he'll take it back. As they start their race, he finally asks for Onoda's name, and, learning that it's "Onoda Sakamichi", declares it a perfect name to go with his. As they race, Manami is overjoyed that Onoda can keep up with his speed on slopes, noticing right away that the wheels of Onoda's bike are holding him back and that his cadence is exceptionally high. This leads him to mistake Onoda for the interesting climber he was told to find. He also notes that Onoda is like him, smiling when going uphill.
Onoda tells Manami that if he wins, not Manami, he'll give the bottle back. Manami replies that he can have it and takes off up the hill at 100m to the summit. Onoda chases after him by dancing, which impresses Manami, and leads him to see that Onoda is not actually wearing cycling shoes to link his feet to the pedals. Manami smiles and sprints up the hill, winning the race. Afterwards, he tells Onoda to just keep the bottle, and watches the boy as he looks over Manami's white road racer. He reflects on how much a difference proper shoes make when riding, and is amazed that Onoda was able to keep up with him while wearing normal sneakers, stating aloud that the boy is indeed amazing.
Before leaving to get back to class before he's late, Manami tells Onoda that he changed his mind and wants his bottle back, but at the Inter-High, declaring it a promise. This promise is part of what fuels Onoda to complete the camp and join Sohoku's Inter-High team. In the anime, Manami is later seen talking to Toudou on his cell phone. Toudou of course thinks Manami is talking about Makishima, and is dumbfounded when he hears about a smiling climber with "short hair and glasses", not an awkwardly smirking climber with long, swaying hair, imagining Makishima has changed his look. Both of them ask who each other is even talking about, equally confused.
F-Group Selection Race
Manami takes part in the F-Group race against Kuroda Yukinari after defeating other team members (notably third-years) to see who claims the second climber spot for Hakone Academy's Inter-High team. He initially is nearly prevented from attending the race by his class rep Miyahara holding him by his class uniform. The girl berates him for sleeping during class and not doing his homework, but he manages to slip away. Manami is the only first-year student to attend the race in the club's history. The race takes place on the "A-course", made out of slopes. Fukutomi Juichi, the team captain, and the other Inter-High members oversee the race from behind in a van, and are seen arguing amongst themselves about Manami and Kuroda, among other things like fangirls.
Kuroda pulls ahead of Manami, but to everyone's confusion, Manami doesn't chase him right away, even after the second-year disappears from sight. Fukutomi ponders about Manami's behavior, wondering what he's feeling. Manami, reflecting on the race, thinks that he loves the feeling of being challenged neck-to-neck, using all his strength, and pushing his body and mind to its limits. To him, it's the only time he feels alive. Putting away his racing gloves, as they're in his way, Manami, with a smile, declares nature as his ally, and that he loves racing because it's so much fun. The members in the van are surprised when Manami suddenly takes off, climbing at high speed up a slope to catch Kuroda.
Once Manami catches up, Kuroda is shaken but thinks he won't be overtaken, since the weaving hills of the area are what he's best at. He tries to keep Manami from passing him, and Fukutomi wonders what Manami will do to win against the more experienced cyclist. Thinking Kuroda definitely has strength and skill, Manami tells him that despite that, he'll be overtaking him on the next curve. Kuroda ignores the psychological attack and rides ahead. At that moment, Fukutomi sees the wind picking up outside the van, and in shock, realizes Manami's plan: he predicted the wind blowing through the mountains. Manami uses it to accelerate and pass Kuroda with ease, feeling alive, and leaving Kuroda far behind, who wonders if he's just witnessed wings on Manami's back. The members in the van are equally left in shock.
As Manami is getting yelled at by Miyahara after the race and looking aloof, Fukutomi tells a reporter that upon gaining its sixth member, his team is possibly the strongest in Hakone Academy's history, and that no schools will rival them at the Inter-High.
Manami is late to the opening ceremony of the Inter-High at Enoshima as the bus with his teammates left him behind. He initially appears riding on his bike and stops at the highway roadblock asking to be let in, though the guard doesn't seem to believe he's a participant, and needs to contact the Inter-High Headquarters. Onoda is already at the opening stage, and is surprised when he sees Hakone Academy's team without Manami there. At the last second, Manami manages to make it to the stage where the rest of his team is standing as winners of the previous Inter-High. The audience wonders why only one of them, Manami, is not wearing cycling shorts, which causes his teammates give him a disapproving look, wondering why he can never be on time. The audience, however, is also surprised to learn he's a first-year.
As the ceremony host begins to ask the team for a word about this year's Inter-High, Onoda makes it to the front of the stage and happily shows Manami he's arrived with the bottle. Manami takes the host's microphone and calls out to Onoda by his first name, confusing the host, who thinks he's talking about hills. While present for Midousuji Akira's challenging of Hakone, Manami doesn't react to him.
Manami is not seen again until the first-day's mountain stage where he pulls the team for Toudou when his senior takes off to race for the mountain check point. As Toudou and Makishima Yusuke start their race once Onoda arrives from his crash to pull his own team, Manami tells Onoda that one day, they should race together like that. He remains with his team throughout the first day, not sent out for any specific purpose.
After the first day's end, Manami brings Toudou to Sohoku's tent so the third-year can thank Onoda for giving him the chance to race Makishima. Onoda and Manami share an awkward few seconds of silence, Manami explaining that they don't have much to talk about when not on their bikes. Once Toudou expresses his gratitude and warns Onoda about how dangerous the second day will be, Manami returns with him to their team.
After the Inter High
Mountain God's Winter Party
Some time during the winter after the 41st Summer Inter High and before his graduation, Toudou is seen mentoring Manami and Onoda at Hakone. He invited them under the guise that there would be a party, but it turns out to be a race to decide which of the two will inherit Toudou's coveted titles of "Mountain God" and "King of the Mountains." Toudou himself does not race, as he states he'd never race in such cold weather. Since the road is full of snow, neither Onoda nor Manami can complete the climb, so Toudou declares that they'll have to settle it at the next Inter High. He scolds Manami for being late at the first Inter High, then tells Manami to give his phone number to Onoda. That way, Onoda can call Manami "on that day" so he won't be late.