WaSuYu interview

"Takahiro: About that, some fans were worried that having the enemies simply retreat would be too plain.
Uezu: Yes, we have to be careful about that in an anime. It's fine to say they just withdrew in written text, but anime is a different case.
We had to figure out in reverse how to insert a climax into those scenes.
Takahiro: And it had to be made in a way that doesn't conflict with the general setting.
Uezu: Plus, we have rules for the battles that we don't want to violate. And despite all that, it still needs to have striking visuals. While keeping these limitations in mind, we came up with the concept that at the time an enemy retreats, a large-scale mechanism utilizing the Great Seto Bridge is set into motion.
Kishi: That is the "flower calming".
Uezu: That's right. As for what is actually being "calmed by flowers", that's a secret for now.
[So this is a particularly powerful, attention-grabbing scene?]
Uezu: Wasn't that Sumi's open-air bath?
Kishi: Hey, come on (laughs)"
Second part of that staff interview TL I posted earlier:

Takahiro: There are also a lot of original parts compared to the novel.
Kishi: That's true, we had to explore every character even deeper than in the novel.
Uezu: I feel like we changed Sonoko a lot for this movie adaption.
[What themes does the movie deal with?]
Takahiro: As one would expect from a movie that has "Friends" as the subtitle and is part of the Yuusha de aru Series, we've worked on it with themes like friendship and a hero's willpower as the foundation.
Uezu: Just like in "Yuuki Yuuna", all of the new girls that make their appearance are very, very good girls.
We draw up situations in which these girls have to overcome difficulties, and it feels like a thought experiment to figure out how they would try to succeed.
What are the things that we want to convey, how do we get the viewers to sympathize with the girls? We want to show their close friendship and the bonds between them.
[What were some difficulties you encountered when you had to adapt the light novel to a movie format?]
Takahiro: "Washio Sumi" wasn't made with the intention to get adapted originally, so I was thinking "it would be a pain to turn this into a movie" when I was writing it. (laughs)
Kishi: Well, it was a pain..... It was really difficult to figure out how to adapt "Washio Sumi".
Whenever there was a problem, I'd consult Takahiro-san right away.
Takahiro: Yeah, we pondered about every element of the work one by one.
Kishi: "If that's what you want to express, you have to do it this way", that's how it went.
I thought it'd be easy to plan it through when we already have the original work - but that's not true at all! (laughs)
Uezu: Even the scenario writing iself took half a year. Because there were many parts that didn't have much of a description, we had to keep that in mind during the work.
Kishi: And in order to keep the intention and the flow of the original work, we had to refine it to perfection in the movie version.
Uezu: Would the plot feel the same or almost like some completely new story? I think adapting from a novel to a movie is really exciting.
[Indeed, you have added music arrangements, battle scenes and various other elements that set it apart from the original work.]
Uezu: That's right. Even though there are many differences to the original work, in the case of visuals, the battles have to follow some rules, so we can't just do what we want.
We had to start with the discussion about what our main objective in drawing a battle was.
Additionally, Sumi and the others had to be weaker than the girls in "Yuuki Yuuna" and there was also the restriction that no matter how much they'd struggle, they could ever only push the Vertex back.
Uezu: Unlike in "Yuuki Yuuna", Sumi and the others display real injuries and we included that in the movie.
I wanted the movie to convey a sense of reality, and to support that idea the fights have to be thrilling.
Takahiro: The fairies in "Yuuki Yuuna" protected the heroes with their barriers, but that's not the case here.
Kishi: Yuuna's team didn't get wounded, but Sumi and the others put their real bodies at stake and get bruised and battered.
Takahiro: I think there were many people who were surprised at how the girls were covered in wounds in the long-awaited bath scene.
The absence of the faires is also a theme of the work.
Kishi: Besides, since the movie would be boring if each of them didn't have a unique fighting style, we had to think a lot about how to set the three apart and how to convey that in practice.

TL source: 4chan