Yūfoniamu Kitauji Kōkō Suisōgaku-bu, Haran no Dainigakushō Kōhen, the film is a spin-off sequel to the television series, focusing on the friendship of Mizore Yoroizuka and Nozomi Kasaki, two supporting characters introduced during the series' second novel (adapted as part of the second season of the anime adaptation).

Atsumi Tanezaki and Nao Tōyama, among others, reprise their voice roles as characters from the television series; most of them were re-designed to better fit the film's style and story.

Liz and the Blue Bird had two composers: Kensuke Ushio, who wrote the minimal-style background music for the high school scenes, and Akito Matsuda, the composer of the television series, who wrote both the background music for the fairy tale segments, and the concert pieces performed by the characters.

Together, the two rehearse a duet from the musical piece Liz and the Blue Bird, which is based on an eponymous, fictional German fairy tale that Nozomi loved as a child.

She stated: "I was moved by the focus [Takeda] placed on developing new characters in that section of the story, and remember becoming captivated with the relationship of Mizore and Nozomi.

Yūfoniamu Kitauji Kōkō Suisōgaku-bu, Haran no Dainigakushō): the first, Zenpen, would be focused on Kumiko, and the second one, Kōhen, on Mizore and her relationship with Nozomi.

[4] Yamada stated about the making of the film: "My first thought was to put my impression of Nozomi and Mizore's story into something visual.

Then, when pulling myself right up-close to the problems and growth the two girls experience, I made sure to catch any small changes or realisations the two may have.

It was a very risky speech style we went for, however we did not intend to make something where the people we show it to simple-mindedly sees them as "very good friends".

Tōyama stated: "Viewers see them from the lateral view, however, from Mizore's perspective, she is always watching Nozomi's back.

[3][8][9][10][11] Unlike A Silent Voice which he joined late during production, Ushio was involved since very early in Liz and the Blue Bird's production, and as such helped Yamada develop her own ideas for the film; he stated: "When I read the script, I thought this was a very personal story; a story that should remain hidden from everyone else.

If such adolescent feelings, so very delicate like glass, were to be known to others, I think that those girls would truly become unable to build connections with others later in life.

[8][9] Talking about the recording of the "Liz and the Blue Bird" piece, Yamada stated "The live performance was just so warm... And I could feel a sense of space.

The boy soprano has this feeling of not being distinctly male or female which I guess really fits in with the film's mix of the subjective and objective."

[13] Liz and the Blue Bird received positive reviews from critics, with most praise going to the relationship and personalities of the two main characters, soundtrack, and animation.

[14] On Metacritic, which assigns a weighted average rating, the film has a score of 67 out of 100 based on 5 critics, indicating "generally favorable reviews".

[15] Natasha H. of IGN gave a highly positive review, stating: that Yamada goes "full out with her own style and approach to constructing an experience of loneliness, misperceptions of people, and overcoming unrealistic dreams.

It is almost impossible to decouple the visual and auditory experiences of Liz and the Blue Bird [...] The soft character designs also lend to emotional expressions, which aligns perfectly with the kind of people Mizore and Nozomi are.

Whether it's the eyes, or slant of the mouth, or even the criss crossing of legs - the attention to detail shows in every frame of the film.

The music is also very particular, as Ushio weaves instruments familiar and strange together into a sparse and discreet score to portray the mindset of the main two characters and atmosphere of each scene in the film."

It displays human insecurity and vulnerability in beautifully honest ways, and thanks to the combined craft of director Yamada's impeccable vision and composer Ushio's sparse but minimalistic soundtrack, it ends up becoming one of the most touching and moving experiences I've seen this year."

[16] Matt Schley of The Japan Times gave the film a 4.5 out of 5 rating, calling it "brilliantly executed" and stating "Not everyone has been in a wind band, but there are few among us who have never had to say goodbye to a friend.

Euphonium fans, Liz will be a welcome trip back into its world, but this film will resonate just as strongly with anyone who's ever been through the emotional roller coaster known as high school.

"[17] Writing for The Daily Dot, Michelle Jarowski gave the film a 4 out of 5 rating, stating "Liz and the Blue Bird soars from the get-go as it weaves together a fantastical fairy tale and a more intimate, relatable high school story.

"[18] Jordan Mintzer of The Hollywood Reporter gave a moderately positive review, unfavourably comparing the film to Yamada's previous work A Silent Voice.

He stated: "Despite the way Yamada keeps reiterating how delicate teenage relationships can be, and how easily they can slip away when you move on to the next stage of your life, the story's limited setting and lack of overt drama makes her movie feel somewhat uneventful.

It seems closer, at times, to an after-school special — or to an episode of Degrassi Junior High — than to a full-fledged feature, even if a late twist gives everything more gravitas.

Aesthetically speaking, there are nonetheless some beautiful moments scattered throughout the story, with the animation switching seamlessly between the detailed manga-style drawings of the classroom scenes and the more ephemeral watercolor renderings of the fairy tale sequences.

Like in A Silent Voice, Yamada has a very keen eye for depicting adolescent malaise in visually evocative terms, and Liz and the Blue Bird could have benefited from even more flights of fancy than she allows for here.

Euphonium: The Movie – Our Promise: A Brand New Day was released on April 19, 2019; it is directed by Tatsuya Ishihara and written by Jukki Hanada, respectively the television series' main director and sole writer.