Episode 5 of "Glass Heart" kicks off with Tenblank immersed in the creation of a fresh tune, while Akane makes a striking transformation, donning vibrant orange hair. Since Kai's departure, they have welcomed a new manager by the name of Gen, who promptly whisks Naoki away for an urgent meeting.
Left behind, the narrative takes a nostalgic detour to a countryside home where Akane, holding Naoki's hand, is on the brink of confessing her deep-seated feelings. However, he abruptly halts her, revealing that his life revolves solely around music, and nothing else. He apologizes and departs, leaving Akane to convince herself that she's perfectly alright.
Post-practice, Akane and Kazushi venture out for a bite to eat, where she opens up about Naoki's rejection, albeit asserting that she's moved past it. Their stroll takes a surprising turn when they stumble upon a poster announcing that Overchrome will be unveiling new material on the very same day as Tenblank. Toya sends Akane the new track, and her heart sinks as she recognizes the melody as an eerie echo of Naoki's latest composition.
Later, in Akane's mother's cozy restaurant, Naoki, Sho, and Kazushi deliberate on the situation. Sho proposes they shield Naoki from the truth and proceed with their track unchanged. Elsewhere, Yukino confronts Isagi, challenging the notion that Naoki penned all her songs, to which Isagi responds coldly, emphasizing her subordinate role. Meanwhile, Toya grows impatient, awaiting Akane's reply.
As dawn breaks, Akane arrives at the recording studio to find her teammates draped in gloom. Naoki has discovered Toya's song and, fuming, canceled their recording session. He asserts that his mind is brimming with melodies and refuses to make a mountain out of this particular molehill.
Akane dashes across town to meet Toya, imploring him to tweak his song, as she understands the immense significance of Tenblank's tune to Naoki. Toya, unyielding, phones Naoki and boldly declares Akane as his. He then whisks her away to his studio, where even Mahiro, Toya's colleague, attests to their innocence in the alleged plagiarism.
Grateful for the timely phone call, Naoki dashes to Toya's studio, urgently beckoning Akane to accompany him. Toya, undeterred, issues a challenge to Naoki: a musical duel where both their compositions will be performed, with the audience serving as the ultimate judge of which tune prevails. The victorious artist will secure the right to release their song. Amidst the preparations, a startling revelation dawns on Akane—Toya and Naoki are half-brothers, united by a common father and both gifted with melodies from Toya's mother. A poignant connection deepens as Naoki recognizes one of Toya's pianos as a relic from their shared childhood, a time marked by an accident where Toya had inadvertently crushed Naoki's fingers with a piano lid. Naoki's fingers dance over the keys, producing a haunting melody that evokes such poignant emotions that even Toya finds himself moved to tears. Before departing, Mahiro solemnly cautions Naoki against using his music as a means to distress Toya.
On their way back, Naoki confesses to Akane his struggle with collaborating effectively with someone he holds in high regard, acknowledging regrets for past actions. Akane reassures him, emphasizing that the members of Tenblank cherish him despite any external misgivings. Together, they aspire to soar to unprecedented heights. When Akane praises the piano composition, Naoki reveals that the second half was influenced by Tenblank's distinctive sound, blending their essence into his work.
Elsewhere, Yukino remains distraught, her creativity stifled by the revelation that Naoki authored all her songs. Her mood shifts slightly when she receives a call from Isagi, who claims to have discovered a means to procure a fresh track for her.
The day of the anticipated showdown between Toya and Naoki finally arrives. In a dramatic twist, Toya, standing in the parking lot, encounters an overzealous fan who, in a fit of adoration gone awry, stabs him.
