Following the release of
Hyrule Warriors (2014) for the
Wii U, fan demands increased for a
Warriors interpretation of the
Fire Emblem series. While working on the expanded release
Hyrule Warriors Legends, its producer Yosuke Hayashi wanted to work on this project, feeling the combat mechanics of the series would be a good fit with a
Warriors title. Once work was completed on
Hyrule Warriors Legends, Hayashi submitted his proposal to
Nintendo and
Fire Emblem developer
Intelligent Systems on a
Fire Emblem-based title, who both accepted. He then talked to director Hiroya Usuda, who was also eager to work on the project. Production was handled by established
Dynasty Warrior developers
Omega Force and
Team Ninja studios, interior teams within
Koei Tecmo. While the core team members of
Hyrule Warriors were carried over, most of the team were chosen by Hayashi based on a request sent through the company for staff who were fans of
Fire Emblem. Intelligent Systems acted as project supervisor for included characters. Nintendo was in the middle of production for the
Nintendo Switch, and at their invitation the team made
Fire Emblem Warriors a multiplatform title for both Switch and
New Nintendo 3DS. Usuda remembered the team being worried whether the Switch would be easy to develop for, but described it as "a very easy hardware to develop for." When choosing gameplay features, the team went through the best-known features of both
Fire Emblem and
Warriors, choosing features that would best fit together. Some features, such as the Weapons Triangle, were difficult to implement and needed adjustment for the action-based combat so players could both be strategic and enjoy the action combat. Notable inclusions from
Fire Emblem were character permadeath, and a "casual" mode which disabled the former feature; the team included both to cater for both casual players and chose seeking a mechanical challenge. To rebalance the gameplay, some characters' weapons were changed such as Lissa from
Awakening using an axe in combat rather than a cane, which was featured as a generic healing instrument. Drawing on their experience designing the horse Epona for
Hyrule Warriors, the team designed the horse-mounted characters to have dedicated combat and abilities. The strategic elements were in part taken from a tactics management system included in
Samurai Warriors: Chronicles and later
Hyrule Warriors Legends; the system had partially inspired the team's wish to create a
Fire Emblem crossover. The game's scenario was co-written by Koei Tecmo's Yuki Ikeno, Ryohei Hayashi, Mari Okamoto and Masahiro Kato. The main plot of gathering gems for the Shield of Flames was directly inspired by the game's theme of different
Fire Emblem characters being drawn together, following series conventions as they had done with
Hyrule Warriors. Some story scenes were decided so they would lead into homages to other
Fire Emblem titles. An early decision was to use young twin protagonists who would strengthen with the help of established characters, with their appearance and dialogue described as an important factor to make the game stand out. Yelena and Darios were incorporated to add a backstory to the twins' narrative, as Usuda and Hayashi felt the twins alone would seem shallow. The character writing was overseen by Intelligent Systems, ensuring that characters would talk to each other convincingly, and that those with intimate relationships would have different ways of speaking appropriate for their partner. When choosing
Fire Emblem characters to feature in the story, the team decided to limit their picks to
New Mystery of the Emblem,
Awakening and
Fates. This narrowed approach was so the team could get a balance of characters with multiple weapons, as choosing only series leads would result in a large number of sword users and unbalance the planned gameplay systems. Character selection was also dictated by which
Fire Emblem games were available worldwide. When including Robin and Corrin, respecting protagonists of
Awakening and Fates who had selectable genders, the team chose their more iconic or popular genders as their default appearance (male for Robin, female for Corrin). Their alternate genders were included as unlockables. Popular characters Lyn from
The Blazing Blade and Celica from
Gaiden were included in other roles. Lyn was the only character included from
The Blazing Blade so the team could focus down onto specific character narratives. Celica was chosen for inclusion over her counterpart Alm to avoid replicas of other
Fire Emblem leads, and to have a magic-focused character. The History Mode was included so more iconic scenes could be included outside the main story. Voice recording for the whole game took three months. The game's art director was Yuta Matsunaga, who was selected by Hayashi from a number of volunteer candidates. The first character designed for both 2D and 3D was
Awakening protagonist Chrom, with Matsunaga saying he needed to get Chrom's design right before the other characters could be designed. Matsunaga needed to strike a balance between the original character designs, the game's graphical design, and input from Intelligent Systems. The twins Rowan and Lianna were designed to appear different from other Lord characters within the
Fire Emblem series. To keep the game's CERO rating low, some characters such as Camilla from
Fates had small clothing redesigns to portray them as "cute" rather than suggestive. Some idle animation poses, such as those of Chrom and Lucina, also needed changing to be more distinct from each other. Lyn's character design was based on both the original character art and her character model from the
Super Smash Bros. series. The original monsters were difficult to design, with early designs being compared negatively by Hayashi to plushies. To fix the issue, the team emphasised their
crustacean-like armor and using colors inspired by poisonous animals. ==Release==