"Aizawa-san Multiplies" centers on Aizawa, a high school student whose life takes an unexpected turn when he encounters multiple versions of himself from parallel universes. These alternate Aizawas, each with distinct personalities, abilities, and backgrounds, begin appearing in his world, creating chaos and confusion. The original Aizawa must navigate this bizarre situation while trying to understand why these duplicates are converging in his reality.

The narrative explores the interactions between the Aizawas, highlighting their contrasting traits and the conflicts that arise from their differing perspectives. Some duplicates are heroic, others mischievous or even antagonistic, leading to a mix of comedic and dramatic situations. As the story progresses, the Aizawas uncover a larger mystery involving the nature of their existence, the multiverse, and the forces that brought them together.

Key characters include the original Aizawa, who serves as the grounded protagonist, and several notable duplicates such as a confident, athletic Aizawa; a genius inventor Aizawa; and a rebellious, anti-authority Aizawa. Their interactions drive much of the plot, as they collaborate, compete, and clash over their shared identity and purpose. The series also introduces supporting characters, including classmates and friends who become entangled in the Aizawas' multiversal predicament.

The plot balances episodic adventures with an overarching storyline, gradually revealing the mechanics of the multiverse and the stakes involved. Themes of identity, self-discovery, and the consequences of choice are woven into the narrative, as the Aizawas grapple with their shared yet divergent lives. The series combines humor, action, and emotional moments, creating a dynamic and engaging exploration of its central premise.