Hiromi Oka starts as an inexperienced high school student joining Nishi High's tennis club, inspired by the graceful star player Reika Ryūzaki, nicknamed "Madame Butterfly." She battles mental fragility, anxiety, and relentless bullying from teammates like Kyoko Otowa, who resents Hiromi's novice inclusion on the varsity squad. Coach Jin Munakata recognizes her latent potential, enforcing grueling training that isolates her from peers while forging resilience through his tough-love approach. Her technical skills evolve from clumsy beginnings to competitive prowess, challenging rivals like Reika and external opponent Ranko Midorikawa.

A romantic tension emerges with boys' tennis member Takayuki Tōdō, though Munakata forbids their relationship during training, forcing Hiromi to prioritize tennis. Her bond with Munakata deepens into unspoken romantic undercurrents. Three years later, Hiromi wins the All Japan Tennis Tournament, earning selection for a New York event. While abroad, Munakata dies of leukemia—a tragedy hidden until her return, triggering a near-catatonic collapse. Her recovery begins at a temple under Katsura, Munakata's former partner, where she shifts from seeking Munakata's approval to self-driven passion for tennis.

Post-recovery, Hiromi confronts a fierce rivalry with Munakata's half-sister Ranko, complicated by shared grief and Ranko's envy over Hiromi's closeness to him. She navigates rekindled feelings for Tōdō, culminating in mutual confession. Rising professionally as a world-class athlete, she balances elite competition with enduring relationships, notably teammate Maki Aikawa's unwavering support. Her journey concludes as a top global player, symbolizing a transformation from fragile novice to self-assured champion through overcoming trauma and sustained mental fortitude.