Tamaki Yamazaki is a Japanese high school student sporting short black hair, typically accented by pink hair pins on each side of her bangs. Her surname signifies "mountain cape/peninsula," while her given name translates to "bead, pearl, gem, jewel princess," hinting at her valued role as a catcher.

Frequent childhood games of catch with her friend Yomi Takeda revealed Yomi's seemingly magical pitching ability. These sessions forged their mutual passion for baseball and a shared promise to keep playing together. The pair separated after elementary school. Throughout junior high, Tamaki honed her skills, becoming a proficient catcher on a competitive team that reached national competitions – an experience contrasting sharply with Yomi's struggles during that same time.

Entering Shin Koshigaya High School brought an unexpected reunion with Yomi. Playing catch again, Tamaki proved capable of handling Yomi's distinctive pitch even with a hardball, reigniting Yomi's enthusiasm for the sport. Tamaki then joined forces with Yomi, the Kawaguchi twins Yoshino and Ibuki, and others to resurrect the school's suspended baseball team, inactive due to a prior scandal.

As the primary catcher for the newly formed team, Tamaki leverages her technical expertise to expertly receive challenging pitches, notably Yomi's high-speed breaking ball with significant trajectory deviation. Beyond her defensive prowess, she contributes as a competent hitter. Working alongside Yomi, she strives to fulfill their childhood promise while driving the team's collective ambition to compete at the national level.