Fanon / Fire Emblem: Three Houses

• A lot of post-game Dimitri fanart depicts him with his NG+ hairstyle (long hair but tied back). Some also like to imagine him wearing his hair like that after Chapter 17, to accompany his return to form.
  • Speaking of NG+ hairstyles, Claude's bandana hairstyle is usually associated with his identity as Khalid/Almyran royalty, while Edelgard's side ponytail hairstyle, just like Dimitri, is also associated with post-game content, specially when in involves Byleth, as well as hypothetical routes where she decides to unite with the other Lords against TWSITD.
• Many stories that bring up Claude's status as an Almyran prince, especially origin stories, will often have him with a different birth name, with Claude either as a middle name or a pseudonym he picked upon moving to Leicester. His own NG+ hairstyle also gets put into use because of said status. This would end up becoming actual canon when the Nintendo Dream Magazine interview revealed that Claude is in fact a false name, and that his real name is Khalid.
• Some fans believe that Byleth stays the same age as they were back in Part I due to Sothis using her powers to place Byleth's body in stasis for 5 years and ages normally after they awaken. In addition, it's also believed that Byleth having full access to Sothis' powers allows them to control the passage of time their body experiences so they can age together with their loved ones in the endings they have with their spouses in non-Crimson Flower routes. Or alternatively, Byleth gives their chosen love interest their blood after merging with Sothis, making them possibly a Child of the Goddess or their love interest receives Rhea's blood so they will age slowly with them, due to the fact that none of Byleth's S-Rank paired endings with human characters mention the death of their love interest.
• With the other Children of the Goddess' transformations appearing to follow The Four Gods (The Immaculate One - Dragon, The Immovable - Tortoise, The Wind Caller - Bird), the only one we don't see Seteth/Cichol's is assumed to be tiger-like to complete the quartet. It's unclear whether Flayn has a Divine Beast form, but due to her love of the ocean and eating fish, some fans imagine a plesiosaur-like sea dragon.
• Many people like to think Claude hatched his white wyvern himself and/or grew up with it. Sometimes the wyvern is also depicted as being isolated/abandoned by its herd due to having albinism.
• In post non-Verdant Wind fanworks, it's common to see Claude coming back as the King of Almyra and forming an alliance with Dimitri/Edelgard and/or Byleth.
• Byleth being able to have as many meals as they have activity points is probably meant to be purely for gameplay, but a lot of fans like to interpret them as actually being a Big Eater and even offer an explanation for why they are like this: they're eating for themselves as well as Sothis. (There is an offhand mention of them eating a lot during a party but it's only the one time.) Three Hopes would confirm that Byleth indeed has a large appetite.
• In Dimitri/Female Byleth post-game fanworks, it's common to depict the pair having a son as their first born child. This was fueled from Gilbert's solo ending where it's stated that he trained the future prince after the war, which many took as confirmation that Dimitri has a son with whomever he marries. Especially notable since most of Dimitri's paired endings don't explicitly mention children.
  • The son is almost always depicted with Dimitri's blonde hair, and will usually look exactly like him. It can be helped further by the fact that Dimitri looks exactly like his own father, Lambert. On top of that, Dimitri's son is usually given the Crest of Blaiddyd mostly because it's funny that he can accidentally break stuff like Dimitri does instead of Byleth's Crest of Flames. Basically, Dimitri's son ends up being more like Dimitri's clone.
  • It's not unusual for their son to be named after Jeralt or Lambert. Or both.
• It's generally assumed by the fanbase that Leonie and Ferdinand, and less commonly Sylvain and Annette, have freckles.
• Some have interpreted Byleth as having a bad knee from an old injury received from their mercenary days, explaining why they only have one poleyn around their left knee.
• The fact the almost all text in the game refers to Byleth with they/them pronouns (or as "the professor" and dodging pronouns entirely when possible)^note Because the game is fully voice acted, differentiating between "he" and "she" would require several hours of extra recordings means many members of the LGBT Fanbase consider them to be nonbinary.
• Dimitri's post-timeskip cape originally belonged to his father.
• Some fanart depicts Byleth with pointed ears after joining souls with Sothis.
• Lots of fanart depicts how Dimitri will carry Byleth after they've merged with Sothis differently based on their gender. He'll just throw Male Byleth like a sack of potatoes over his shoulder, but does a gentler Bridal Carry for the female. It would make sense given his personality, especially after he says an apology to his unconscious female professor before picking her up. This is one of the few times the game doesn't use Gender-Inclusive Writing. All of the house leaders have different lines for this particular scene,◊ and Dimitri is the only one that carries them himself. The other house leaders sometimes volunteer someone else. Nothing is said about how Byleth was carried back, just that they were.
  • This is treated as a very romantic scene for many Female Byleth/Dimitri fanworks because of how inherently intimate it is.
• In part because neither character is ever shown on screen, most fan interpretations of Holst and Glenn tend to carry the same elements. Holst is generally pink-haired and as muscle-bound as Balthus, though on occasion Holst will lack those muscles. Glenn tends to have Felix and Rodrigue's long blue hair and generally looks like Felix if he lightened up or a younger version of Rodrigue. So basically clones of their younger siblings. Three Hopes would go on to confirm that Holst was indeed a pink-haired, muscle-bound man.
• Some have taken to interpreted Byleth as being autistic as some of their behavior does line up with similar behaviors among those on the spectrum.
• Due to a line said by Ferdinand, where he refers to himself as the only legitimate son of Duke Aegir, a number of players believe that Ferdinand has half-siblings, and calls himself the only legitimate one as a way of indicating his status or position for those who may assume otherwise. As part of this, there exists a somewhat popular fan idea that Kronya is Ferdinand's half-sister, pointing to said line, Kronya's orange hair, and the implication of Duke Aegir working with TWSITD. Of course none of this is actually supported in game, but it remains a popular idea.
• Despite Silver Snow being the intended default route for the Black Eagles (and the game in general), very few fans consider it such, instead treating Crimson Flower as the Black Eagles route, with Silver Snow usually referred to as the Church Route. To wit, Ao3 defaults the "Crimson Flower" tag to "Fire Emblem: Three Houses Black Eagles Route".
• The idea that Hilda hates Edelgard or is jealous of is common in the fandom due to Hilda being unrecruitable on only the Crimson Flower route in Three Houses, and unable to fight alongside Edelgard in Three Hopes, despite both games having scenarios where Claude and the Alliance can work with Edelgard. There's little in-game evidence of Hilda holding any strong opinions towards her, and she's always initially reluctant when recruited outside of the Alliance, but it's often seen in fan works and memes, whether Played for Laughs or Drama.
• Thanks to Marianne mentioning in her support conversations with Byleth that back before the Time Skip she regularly prayed to die and grew out of that self-loathing thanks to Byleth, a decent amount of the fandom thinks that she doesn't appear post-timeskip if she wasn't recruited beforehand because without Byleth's influence, she commits suicide. The game doesn't outright say why she doesn't appear, beyond her fate if defeated on Classic difficulty pre-timeskip being that she simply rode away one day and was never seen again. Some see this as the game alluding to her killing herself without saying so outright, though the game does also establish that Margrave Edmund holing up and waiting out the fighting would be like him, with no reason why Marianne couldn't be with him.
• Sylvain's biggest growth weakness is his dexterity, and his only bane is in bows. This alongside him saying that him hitting on a scarecrow was an accident has led to some fans believing that he doesn't have good eyesight.
• Throughout fan discussion, it's incredibly common to see the Children of the Goddess referred to as "Nabateans". This seems to stem from a cutscene on the secret route, in which Rhea, her mental state unravelling, vows vengeance "in the name of the Nabateans"; a great many players manage to stumble onto the secret route on their first playthrough but don't end up jumping through the additional hoops to get the alternate version of that cutscene, in which the term Nabatean is not used.