Three non-playable characters in Fire Emblem: Three Houses - Rhea, Sothis, and Jeralt - have many unused quotes that depict them being fully playable in battle. These include character selection, battle grunts, critical hits, gambits, victory, leveling-up, and other types of quotes. Though some of these are used by Rhea and Jeralt when they appear as non-playable characters in battle, there are some that cannot be viewed, and Jeralt, in particular, has unique critical hit and victory quotes that differ from his appearance as a non-playable character.
Unused dialogue indicates that Lorenz can be encounted as an enemy unit during Chapter 16 of the Verdant Wind route. During the same chapter in the Silver Snow and Azure Moon routes, Lorenz is encounted as an enemy, and as such most of his battle quotes are recycled from those routes. However, there is an unused quote where Claude can fight Lorenz.
There exists unused dialogue between Ferdinand and Lorenz for the Dining Hall which would've been used when both characters have reached A-Support with each other, an impossible feat in the final product as their support chain ends at B.
Lorenz: To share a table with you is a comfort in these difficult times.
Ferdinand: I feel precisely the same, Lorenz. Such cheerful moments give me the will to keep going.
Since mostly every unit can potentialy ask 2 questions, one in the academy phase and one the war phase, Gilbert falls into this category but since he only joins during the war phase in Azure Moon, His academy phase question is unused without hacking him in to your roster during the academy phase. Also despite being the only unit not to ask questions during a lecture, Jeritza has leftover dialogue when he asks a question and having different responses to a question but they remain unused.
For the purpose of educating young aristocrats, the church borrows a number of soldiers from each country. As these soldiers from different origins gather in one place, animosity and fighting become frequent. It is...a problem. (Joined by Seteth and Alois)
"Help the soldiers socialize. It's harder to fight a friend." (Neutral answer for Gilbert, Good answer for Seteth and Alois)
"Keep the troops separated. Fighting is for the battlefield."(Good answer for Gilbert, Neutral answer for Alois, Bad answer for Seteth)
"Some conflicts are inevitable."(Neutral answer for Seteth, Bad answer for Gilbert and Alois)
Gilbert and Jeritza list their personal history for both Part I and Part II, as with all of the playable characters, but both can only be recruited during Part II and as a result, their Part I personal history is left unused. However, Gilbert’s part 1 personal history table can be viewed in normal gameplay if one has purchase the Cindred Shadows DLC and finished the quest Roster Retrieval, it can be viewed in normal gameplay.
Two unused endings exist in the game's code that remains unused in the game. The first is Gilbert in the Azure Moon route, who has an unused ending if he falls in battle during Part I in Classic Mode. However, Gilbert is only recruitable after the time-skip and as such cannot fall in battle prior to this. The second is Byleth and Hilda sharing an ending in the Crimson Flower route, but Hilda cannot be recruited in this route, as she can only transfer to the Black Eagles house if the player sides with the Church of Seiros in Chapter 11.
"Wounded in the coup of Fhirdiad Harpstring Moon, 1181. Died of his wounds soon after the war."
Byleth, Wings of Hegemon & Hilda, Free Spirit
"Almost immediately after Byleth and Hilda finished their gorgeous wedding ceremony, the struggle against those who slither in the dark began in earnest. They fought tirelessly to bring lasting peace to Fódlan, and afterward retired from the Imperial army to Goneril territory. Hilda's hobby of creating fashionable accessories bore fruit, and she leveraged her husband's reputation as a hero to create the first artisan academy in Fódlan. The school produced many talented craftsmen, one of whom created a statue that expertly captured the hero's delight at receiving the gift of a bracelet from his wife."
Seteth, Flayn, Catherine and Cyril have a variation of their S-Support's illustration with Byleth, in which the latter has their original hair color. However, the four characters cannot be recruited into the Crimson Flower route and as such cannot reach this ending.
Additionally, an alternate version of an illustration of Zanado was created, featuring Sothis in her original form. This was later redone to have a generic Nabatean priest standing where Sothis would be, and the unused artwork can be briefly seen during the game's opening, albeit with various effects.