"The Tatami Galaxy" centers on an unnamed university student navigating his college life, grappling with regrets and the pursuit of an idealized romantic and social experience. The narrative unfolds through a repetitive structure, with each episode resetting the timeline to the protagonist's first day of university. In each iteration, he joins a different student club, hoping to find fulfillment, love, and a sense of purpose. However, his choices consistently lead to disappointment, as his insecurities, indecisiveness, and tendency to blame others for his failures hinder his growth.

The protagonist's journey is deeply intertwined with his relationships, particularly with his enigmatic friend Ozu, who often manipulates situations to his advantage, and Akashi, a sharp-witted underclassman he admires. Despite his efforts to win Akashi's affection, his self-sabotaging behavior and inability to confront his flaws repeatedly thwart his chances. The series explores themes of regret, self-awareness, and the passage of time, as the protagonist reflects on his choices and their consequences.

As the story progresses, the repetitive cycles begin to converge, revealing a deeper narrative about the nature of happiness and the importance of living authentically. The protagonist's journey culminates in a moment of clarity, where he confronts his past decisions and gains a newfound perspective on life. The series blends surreal visuals, philosophical undertones, and a nonlinear narrative to create a thought-provoking exploration of youth, identity, and the pursuit of meaning.