Questions are roughly translated and answers are mostly paraphrased. I've skipped some questions that I didn't feel were important. For the author's interview for the movie premier, see here
This interview does have movie spoilers for those who want to avoid them
Interview[]
"I've heard that this is your first anime script"
The author asked his editor if they'd allow him to write it and the movie staff readily agreed to his request. He states that he felt motivated by the thought that people would come to the theater to watch since he'd done the same as a child. He admits that there are parts that clashes with preexisting stuff but makes the excuse that it's a movie
It's noted that the Masara Fruit and leaving Orario on dragons in the movie is a homage to an anime movie the author watched as a child, which I assume is Arion based on a quick search but I'm not sure (in said movie they're apparently Pegasuses)
"What do you mean it clashes?"
Dragons don't listen to orders but the author wanted Bell and the others to fly so he let it happen. He states that he accomplished this by having them raise the dragons since they were born and imprinting them. He feels it wouldn't be good to be too strict about light novel settings when it comes to the anime, something he felt when he was a part of the anime
"How was it like talking things over with the movie staff?"
The author states that made progress on various things through discussion, like Artemis, who was a somewhat vague character in the beginning. He admits he originally wanted to redo episode 13's Black Goliath battle, claiming that things could've been better if he had 10 more minutes, but was convinced by the author to do a movie about Bell and Artemis
It's noted below that they made sure to not portray Artemis differently than planned, and if something was different, they went over it and fixed it, such as make sure not to accidentally portray her as a dislikable character. The producer told him that "anime producers are people that arranged songs that were written and composed" and that this movie was "a shoujo manga"
"What do you mean by "shoujo manga"?"
The author reveals that they went with a Jo-ha-kyū structure rather than a Kishōtenketsu one. He feels that Bell and Artemis strengthening their bonds was like a shoujo manga and feels that the producer took his "maiden circuits or something like that" into consideration. He adds that he isn't good at writing love comedy, but things sometimes went well when he thought of love as a shoujo manga
"Was there anything else you intended to do?"
The author states that he didn't want to make something new but rather something that'd state "this is what DanMachi is" to people that've watched the anime before or people that are watching it for the first time in theaters. He added scenes that were similar to the main series/spinoff like Lili's indirect kiss and peeking.
"The peeking ended up being large scale"
Just before the kyu part of "johakyu", the author added the peeking scene in order to prevent things from becoming too serious. He adds that the scene laid the foundations to deepen Bell and Artemis' relationship
"Freya appeared in the movie as well"
The author feels that Loki and Freya wouldn't have been able to solve the matter in the movie, and that it would've required Artemis and the person that was chosen by the Arrow of Orion. The characters that grasped the entire situation were Hermes (who first contacted Artemis), Ouranos (who received the report), and Ganesha. He adds that Hermes didn't try to forcefully solve it, but rather set up a path to save Artemis (considering they're from the same area in heaven), and feels that there wasn't anything behind his intentions other than wanting to prepare a path to save a crying girl
"So you're saying he had special feelings for Artemis?"
"They're most likely not feelings of love". The author states that seeing Artemis act different shocked Hermes but made him feel joy that she'd become able to love someone. His "I want to save her" feeling most likely came from seeing his pitiful friend and was most likely out of friendship
"Tell me more about the settings"
The author states that he had Welf hear about "Divinely Created Weapons" from Hephaestus. When thinking of why it couldn't be Ais, he decided that they had to be "chosen", which is how he came up with the idea. He considered the idea for the main story but added it to the movie since he was able to (I'm not sure if he's implying that said weapons will appear in the main story)
It's noted below that the Arrow of Orion is covered in hieroglyphs and they do mean something if you decode it, and apparently its somewhat of a spoiler. Also, "the way Lili used her magic sword (lightning) is something I wanted to put in the main story but was used in the movie first"
"What exactly is Orion?"
The author decided from the beginning that Artemis' "Divinely Created Weapon" would be named Orion, and since it has the her remaining thoughts, it would take someone whose soul was like hers to wield it. Bell was an existence similar to Artemis' other self, which was why she called him Orion
"So you didn't get into detail about it"
The author wanted to add a bit about the core of the DanMachi story and not just Artemis, but had to remove some stuff when he considered time and movie flow. Originally, after Lili said "Do something about it" to Hestia (meaning Hestia and the other Gods), he planned to have Hestia say "We (the Gods) can't defeat that monster" and include something that would foreshadow why, but didn't. He also planned to have Bell say "Is that the Black Goliath from before?" but scrapped it, and adds that this is a "bomb class" foreshadowing
It's noted below about the author's comment concerning "Black Monsters" and it hints that readers might be able to perceive the deeper part of the story if they look for what they have in common
"Was there something you struggled with concerning the script?"
The author reveals that he struggled with explaining things since its a different medium, it's not like the novel where he could take as long as he needed to explain things. He struggled with explaining Artemis, Antares, and "Divinely Created Weapons".
"I've heard you wrote a prequel of the movie"
The author mentions that he wanted to write about how strong Artemis was as a Goddess in the bonus SS, and also mentions the DanMemo prequel story as a prequel from a different viewpoint