A small-town elementary school teacher with no political experience or ambition is thrust into the heart of national leadership. Keita Asakura is a fifth-grade teacher in the Nagano prefecture, a man far more interested in astronomy and the well-being of his students than in the world of politics, which he despises for having consumed his absentee father. However, his life is upended following a plane crash that kills his father, a sitting member of the House of Representatives, and his older brother, the heir apparent to the family's political seat. Facing a critical by-election, the ruling party's powerful secretary general, Shoichi Kanbayashi, and his sharp, ambitious secretary, Rika Miyama, devise a plan. They see Keita as a perfect, pliable stand-in to maintain the party's hold on the district.

Initially a staunch refuser, Keita reluctantly agrees to run only to prevent his mother from being dragged into the race. He returns to his family's home district in Fukuoka, a complete political novice, and is met by a seasoned and eccentric election strategist, Katsutoshi Nirasawa, who lives by the credo that "election is the only war permitted by law". With Nirasawa's tactical genius and Rika's stern guidance, the honest and unconventional Keita runs a sincere campaign, refusing to sling mud despite attacks regarding his father's past corruption scandal. To everyone's shock, this political outsider wins a narrow but stunning victory, taking his father's seat in the national Diet and earning the media nickname "the Prince of Congress".

Keita's improbable ascent does not stop there. The sitting prime minister resigns amid a scandal, and the party bosses, led by the manipulative Kanbayashi, see an opportunity. They decide to make the wildly popular Keita the face of the party, calculating that his high approval ratings will win them a general election, after which he can serve as a puppet prime minister while Kanbayashi pulls the strings from the shadows. Keita agrees to run for party president and, through a series of heartfelt speeches that resonate with a disillusioned public, wins in a landslide, becoming the youngest prime minister in Japanese history.

The series then follows Keita's tumultuous tenure as he discovers that being a leader means far more than giving speeches. He is immediately bogged down by bureaucracy, security details, and a cabinet hand-picked by Kanbayashi that seeks to isolate him. While Kanbayashi and his cronies expect him to simply rubber-stamp their decisions, Keita, guided by his common sense and a desire to truly help people, begins to push back. He prioritizes child healthcare over a party-backed dam project, works through the night to understand budget proposals, and makes a point of personally investigating issues. This leads to a deep ideological conflict with his own party, forcing Rika, who is torn between her loyalty to Kanbayashi and her growing respect for Keita, to make difficult choices.

After surviving numerous scandals, cabinet resignations, and a health collapse brought on by overwork, Keita's resolve culminates in a final, dramatic confrontation with the political establishment. Facing a vote of no confidence, he bypasses the traditional backroom dealing and addresses the nation directly in a lengthy, unscripted live broadcast. In this speech, he sheds the formalities of his office, laying bare the corruption, the struggles of ordinary citizens, and his own failures and dreams for the country's future. This moment of radical transparency allows Keita to outmaneuver his rivals not with political cunning, but with sheer moral conviction, fundamentally challenging the nature of power itself.