In the opening episode of "Glass Heart," Saijo Akane finds herself unceremoniously dismissed from her band amidst the electric atmosphere of a bustling music festival. Her bandmates reveal a harsh truth: their agency insists on maintaining a masculine image for their rock band, leaving no room for her. As fate would have it, a thunderstorm unleashes its fury, prompting the evacuation of the spectators.
Amidst the chaotic exodus and relentless downpour, Akane finds solace at her drum set. She seats herself and begins to play, her beats echoing against the stormy backdrop. Moments later, a mesmerizing symphony ensues as a man on stage joins in on the keyboard, crafting a medley that captivates all who hear it. Tragically, this harmonious moment is shattered when Fujitani Naoki, the keyboardist, is struck by lightning in a dramatic twist.
Cut to three years later, where Akane and two fellow musicians audition at a studio, only to receive a disappointing rejection later. The criticism stings: her drumming lacks the sensitivity required. Back at her mother's restaurant, Akane learns from her mom about Fujitani Naoki's mysterious reemergence with a new band, despite having vanished after his lightning strike. Disheartened by her relentless efforts over the past three years, Akane concedes defeat on her lifelong dream.
On a delivery run for her mother, Akane stumbles upon an intriguing note inviting her inside a house. Following the haunting melody of a piano—a haunting echo from the festival—she discovers Naoki, playing his keyboard once more. Soon, renowned guitarist Takaoka Sho and internet sensation Sakamoto Kazushi enter, each picking up their respective instruments to create a symphony once more. Akane, unable to resist, joins in on the drums, the rhythm of her heart resonating with the music.
Later, Akane shares her unexpected invitation to join a band with her college friend. After class dismisses, she finds Naoki awaiting her outside. They meet Kai, Naoki's manager, who flatly refuses to entertain the idea of Akane joining the band. Undeterred, Naoki vows to prove that Akane's inclusion is a necessity. He reveals their upcoming gig as the opening act for Overchrome in a week and hands out the songs for them to practice.
The scene is set, the stakes raised, and Akane stands at the crossroads of her dreams and reality, poised to either reclaim her passion or surrender to the whims of fate.
Akane diligently applies herself to her craft, her passion undiminished. One fateful day, she stumbles upon Kazushi, who is mesmerizingly rendering an impromptu version of "Für Elise" on the piano. Akane lavishes him with praise, but he, in turn, critiques her drumming, suggesting a lack of finesse and hinting that perhaps she should reconsider her role if she acknowledges her own shortcomings. Undeterred, Naoki then leads Akane to an exhilarating Overchrome rock concert, where the electric energy of the music ignites the atmosphere.
Post-concert, Naoki seeks out Toya, the lead singer, backstage. An underlying tension crackles between them, and Toya, sensing an opportunity, challenges Akane on her confidence to jam alongside Naoki. Akane admits her hesitation but expresses her determination to reach that level of assurance. Naoki, taken aback by her honesty, abruptly excuses himself, leaving the scene.
Consumed by worry that she may have disappointed him, Akane embarks on a search for Naoki. Her quest leads her to a secluded corner where Naoki sits solitary in the rain, leaning against a wall now adorned with hastily scribbled musical notes—the blueprint of a nascent composition. Far from being disheartened by her earlier admission, Naoki finds solace in Akane's unwavering ambition and drive.
Practice sessions resume with renewed vigor. However, during one intense rehearsal, Naoki collapses, exhaustion taking its toll. Upon regaining consciousness, he reveals to Akane that it was her drumming during the music festival that awakened a long-dormant resonance within him, a sound he had thought lost forever.
The long-awaited concert day dawns. With hearts pounding and spirits soaring, the group ascends the stage. Naoki introduces them with pride, announcing their name to the eager crowd: Tenblank.
