Eiji Kurahashi is the left-handed pitching ace for the struggling Seishū High baseball team, having been one of Japan's top middle school pitchers. He lives with his truck driver father, and their relationship grows strained when his father forbids him from playing baseball in high school. This prohibition leads Kurahashi to troubling actions, including stealing women's underwear from a clothesline. Teammates Katsuya Niimi and Susumu Karasawa attribute this behavior to pent-up frustration from lacking baseball as an outlet, calling it "filthy stuff."

Niimi and Karasawa intervene, confronting Kurahashi's father. Niimi's father shares his positive high school baseball experiences, emphasizing how it builds perseverance and resilience for adulthood, not just competition. This helps reconcile father and son, leading the father to relent and allow Kurahashi to join the team.

As a player, Kurahashi becomes the technical and tactical cornerstone of the team's improvement, ending their losing streak. While also quietly mediating the group's personal relationships, he functions as an observant "love doctor." He orchestrates romantic opportunities for teammates, offers relationship guidance, and subtly influences interpersonal dynamics, particularly regarding the romantic tensions involving Katsuya Niimi, Yuri Nakao, and Yukimi Yasuda. This contrasts with his earlier implication in an unconfirmed train groping incident.

His development centers on baseball providing a constructive channel for his energies, resolving his earlier behavioral issues. He consistently maintains a calm, collected, and observant demeanor, contributing significantly as a skilled pitcher on the field and through his mediation off the field.