On the eve of the Tanabata festival, a shy and socially awkward young man named Tsuyoshi Yamada is riding the train home to his modest Tokyo apartment. An otaku whose life revolves around anime, video games, and collecting figurines, Yamada spends most of his free time in his cluttered bedroom, far from the world of romance and social grace. On this particular night, he witnesses a drunken man harassing a beautiful and elegant woman, Saori Aoyama, and her friend. Despite his crippling shyness, Yamada musters the courage to confront the drunkard and chase him off the train. The woman thanks him politely before the two part ways.

Deeply affected by the encounter, Yamada posts a detailed account of the incident on an internet message board for lonely singles. He calls the woman "Hermes" after the expensive teacups he imagines a woman of her class might own. The anonymous and eccentric members of the board, who have nicknamed him "Densha Otoko" or "Train Man," become his unexpected support group. They encourage him to take the next step when a package arrives at his apartment: a pair of expensive Hermès teacups, a thank-you gift from Saori. His online friends cheer him on, offering advice on everything from what to wear to how to make a phone call without stammering.

As Yamada nervously follows their guidance, he and Saori begin an awkward, tentative courtship, going on dates to art museums and restaurants far outside his usual world. The members of the chat room, who include a nurse, a college student, a corporate worker, and a shut-in, live vicariously through his progress. Their own personal struggles are mirrored in Yamada's quest, and his small victories give them hope for their own lives. However, the path to love is filled with misunderstandings and setbacks. Yamada's lack of confidence and his fear of revealing his otaku lifestyle to the refined Saori threaten to derail the relationship, leading to painful moments of embarrassment and near-collapse.

The central narrative arc follows Yamada's transformation from a self-deprecating recluse into a young man capable of genuine connection. The online community, in turn, evolves from a collection of cynical strangers into a tight-knit group whose encouragement for Densha Otoko inspires them to face their own real-world challenges. After a dramatic falling out, Yamada makes a grand, public gesture to win back Saori, proving he has internalized the courage he once only borrowed from his online friends. In the end, he reconciles with Saori not by abandoning his otaku identity, but by integrating it with his newfound self-confidence, demonstrating that he can be true to his passions while also opening his heart to another person.