On a chilly March night just before the start of a new academic year at Kansei University in western Tokyo, a former high school track star named Kakeru Kurahara runs through the city streets after shoplifting bread. Though disillusioned with the sport that once defined him, he feels like he could run forever. His flight is interrupted by a mysterious boy on a bicycle, Haiji Kiyose, a fellow student and runner who has been following him. Impressed by Kakeru's natural agility and speed, Haiji persuades the reluctant Kakeru to move into Chikusei-so, a notoriously run-down and cheap dormitory near campus where Haiji resides with eight other students.

Kakeru soon learns that Chikusei-so is the historic former home of the university's track and field team. At his welcoming party, Haiji reveals his grand and seemingly impossible plan: to assemble a ten-man team from the dormitory's residents to compete in the Hakone Ekiden, one of Japan's most prestigious and grueling university relay marathons. The race takes place over two days during the New Year's holiday, covering more than 200 kilometers from central Tokyo to the mountain town of Hakone and back, divided into ten challenging sections.

The eight other residents are not just non-runners; they are complete novices with no interest in athletics. The group includes Takashi "Shindo," an earnest honor student from the mountains; identical twins Jota and Joji, who are more interested in attracting girls; Yuki, a detail-oriented law student who passed the bar exam on his first try; "King," a trivia-loving senior preoccupied with fruitless job hunting; Musa Kamala, a kind and earnest international student from Tanzania; "Nico-senpai," an older student and heavy smoker who ran in high school; and "Prince," a manga otaku with almost zero physical stamina.

Despite their reservations and Haiji's overbearing enthusiasm, one by one, the residents are won over. Takashi is the first to be convinced, while the twins agree when told running will help them with girls. Nico hopes the training will help him quit smoking, and King sees the famous race as a way to stand out to potential employers. Prince, the slowest and most reluctant, is eventually spurred on by the group's growing camaraderie. With approximately ten months to prepare, Haiji becomes the team's de facto coach and strategist, creating a tailored training regimen for each member while hiding his own painful past and a serious knee injury that threatens his ability to run at all. The official landlord of Chikusei-so acts as their coach in name only, leaving the real work to Haiji.

The narrative follows the team through the highs and lows of their intense training, from building individual endurance to competing in record meets. Kakeru struggles to overcome the disillusionment and guilt stemming from a violent incident on his high school team, while Haiji pushes his own damaged body to its absolute limit to keep his dream alive. As they prepare, the team bonds, overcoming personal demons and learning the true meaning of running not for oneself, but for others. Through a combination of Kakeru's prodigious talent, Haiji's strategic mind, and the collective will of the group, they achieve a miracle and qualify for the Hakone Ekiden.

The climax of the story is the race itself, where each of the ten runners must face their own limits on their assigned leg. During the Hakone Ekiden, Kakeru shatters a section record, and Haiji, running in immense pain, delivers a heroic performance. The team ultimately finishes in tenth place, an extraordinary achievement for a first-time, unsponsored team that secures their automatic entry for the following year and cements their bond as they cross the finish line together.