Mizore is a reserved and introverted student in her senior year of high school, who plays the oboe in the school's concert band. The person who occupies her thoughts the most is her best friend, Nozomi, one of the flutists in the band, who shines with her outgoing and charismatic personality. Together, the two girls practice a duet from the musical piece Liz and the Blue Bird, which is inspired by a fictional German fairy tale beloved by Nozomi during her childhood. This poignant tale tells of a young woman named Liz, represented by the oboe, and a mystical blue bird that transforms into a human, symbolized by the flute. Their deep friendship faces an inevitable separation, mirroring Mizore's worries about her own relationship with Nozomi as they approach graduation.
As Mizore navigates her feelings, she finds herself increasingly isolated from her classmates, willingly declining the invitations of her fellow bandmates to spend time together. Her heart is heavy with emotions she struggles to articulate to Nozomi, even as Niiyama, their dedicated woodwind instructor, encourages her to consider pursuing music professionally after graduation. Initially dismissive of this idea, Mizore’s perspective shifts dramatically when Nozomi expresses interest in applying to the same music school, making Mizore feel a renewed sense of purpose, albeit driven primarily by her attachment to Nozomi. This concern does not go unnoticed by their peers, who fear that Mizore's motivation stems only from Nozomi's influence, who may not genuinely pursue a career in music herself.
As the concert draws near, tension escalates between Mizore and Nozomi. Mizore's anxieties amplify as she recalls past incidents where Nozomi distanced herself from the band. Meanwhile, Nozomi struggles with her own emotions as Mizore opens up to more friends and improves under Niiyama's guidance, fueling her envy over Mizore's evident potential. Their rehearsals become increasingly strained, particularly around the emotional depth of their duet, as Mizore grapples with the notion of why Liz would let the blue bird fly free instead of holding onto it forever.
Thanks to the diligent support from Niiyama and their bandmates, Mizore and Nozomi gain clarity about their relationship. They come to understand that while Mizore initially identified with Liz, and Nozomi with the blue bird, it is, in fact, Mizore who embodies the free spirit of the bird—she must learn to release her dependencies to truly thrive—while Nozomi fits the role of Liz, who sacrifices her desires for the sake of the blue bird’s freedom. The pivotal moment arises during their next rehearsal, where a passionate performance leaves their fellow band members in awe, while Nozomi steps out in tears, deeply affected by Mizore's emotional resonance.
In an intimate conversation post-rehearsal, Nozomi confides in Mizore, acknowledging her awareness that Mizore has been tempering her own talent to support her. She admits that her earlier claims about applying for music school sprang from jealousy regarding Mizore’s abilities rather than a true ambition of her own, revealing a starkly different reality. Mizore, frustrated by what feels like a disregard for her own feelings, wraps her arms around Nozomi and pours out her heart, expressing the true depths of her affection. However, Nozomi chuckles, understanding that acknowledging Mizore's love would only serve to bind them further.
As time passes, it appears that the distance between Mizore and Nozomi lingers. Nozomi tends to her entrance exams, seemingly deprioritizing their band relationship. A pivotal encounter in the library leads to Nozomi inviting Mizore to a café after school. On their way, she assures Mizore that she will flawlessly support her in their duet but asks for "a little time." In response, Mizore affirms her commitment to continue playing the oboe. As they stroll together, an unexpected moment occurs when Nozomi turns sharply to look at Mizore, leaving her visibly surprised.
