"Mix: Meisei Story" is a sports anime centered around baseball, set in the same universe as Mitsuru Adachi's earlier work, "Touch." The story takes place at Meisei High School, a once-prestigious baseball institution that has fallen into decline. The narrative revolves around two stepbrothers, Touma and Souichirou Tachibana, who share a passion for baseball and aspire to revive their school's team to compete in the prestigious Koshien tournament.

Touma, the older brother, is a talented pitcher with a calm and collected demeanor, while Souichirou, the younger brother, is an energetic and skilled batter. Despite their contrasting personalities, the brothers share a deep bond and a mutual dream of achieving greatness in baseball. Their journey is intertwined with the legacy of their fathers, who were also brothers and former Meisei baseball stars. The brothers' fathers, along with their mother, passed away in a tragic accident, leaving the boys to grow up together under the care of their uncle.

The series explores the brothers' efforts to rebuild Meisei's baseball team, facing challenges such as a lack of experienced players, internal team dynamics, and formidable rival schools. Along the way, they encounter a diverse cast of teammates, each with their own struggles and motivations, contributing to the team's growth. The narrative balances the brothers' personal development with their pursuit of athletic excellence, emphasizing themes of perseverance, teamwork, and familial bonds.

As the story progresses, the brothers navigate the pressures of high school life, relationships, and the weight of their shared history. Their journey is marked by intense training, strategic gameplay, and emotional moments that highlight their determination to honor their fathers' legacy while carving out their own path. The series captures the essence of high school baseball, blending competitive sports action with heartfelt character-driven storytelling.