In 1951, postwar Japan, a young mathematician named Andy Homura dedicates himself to solving Fermat's Last Theorem, a problem that has eluded the world’s finest minds for over three hundred years. His solitary pursuit is upended by the sudden appearance of a girl named Rama, a prodigy whose raw mathematical intuition far exceeds anything Homura has encountered. Her presence reshapes his approach and sets in motion a chain of events that draws other gifted mathematicians into the orbit of the legendary problem.

Homura’s quest soon attracts the attention of two more mathematicians, Rōa and Enjirō, who recognize the value of notes that Rama has scribbled on scrap paper. In exchange for their help deciphering those notes, Homura invites them to collaborate on the proof. Meanwhile, the traditional Japanese mathematician Tōroku, a specialist in wasan (Japanese mathematics), suggests that wasan may have advanced further than Western approaches in certain areas relevant to the theorem. This insight pushes Homura to consider an unorthodox geometric path, one that most previous challengers had dismissed. Volume by volume, the team tests every possible angle, and Homura confronts the enormous gap between his own abilities and Rama’s seemingly effortless genius. The story culminates in the completion of the first major arc of their shared mathematical journey.