Although Byleth’s sexuality is determined by the player’s actions, other characters have support conversations or paired endings without Byleth that imply or confirm their queerness. The list below goes into details about each specific character who is implied or confirmed to be queer in some way:

• Dimitri: He has three same-sex paired endings, with none explicitly ending in romance or marriage, but his ending with Dedue could imply queerness in that they were family in private and were buried next to each other. There is also no mention of a queen or children in this ending specifically. We have classified him as Bisexual Implicit.
• Hubert: He has one same-sex paired ending which does not explicitly mention romance or marriage, but his A+ support with Ferdinand heavily implies feelings for each other. We have classified him as Bisexual Implicit.
• Ferdinand: He has one same-sex paired ending which does not explicitly mention romance or marriage, but his A+ support with Hubert heavily implies feelings for each other. We have classified him as Bisexual Implicit.
• Caspar: He has two same-sex paired endings; one does not imply any romance or marriage while the other, his ending with Linhardt, mentions settling down with him. We have classified him as Bisexual Implicit.
• Petra: She has one same-sex paired ending with Dorothea which explicitly mentions love. We have classified her as Bisexual Explicit.
• Dedue: He has two same-sex paired endings, with none explicitly ending in romance or marriage, but his ending with Dimitri could imply queerness in that they were family in private and were buried next to each other.
• Felix: He has two same-sex paired endings, with both possibly implying romantic feelings. His ending with Dimitri mentions him feeling more grief than the queen at Dimitri’s passing while his ending with Sylvain on a Blue Lions route mentions the two growing so close that “they passed away on the same day, as if conceding that one could not live with the other”. He also has a quote during a visit to the Goddess Tower with F!Byleth that he’ll always feel more comfortable holding a sword than a woman’s hand. In the same conversation he also says he has no interest in love or romance. We have classified him as Asexual and Bisexual Implicit.
• Sylvain: He has one same-sex paired ending with Felix which does not explicitly mention love or marriage. However, the Blue Lions route version mentions the two growing so close that “they passed away on the same day, as if conceding that one could not live with the other”. Additionally, in the original Japanese text of his C-rank support with Ingrid, Ingrid mentions him accidentally hitting on a crossdresser, to which a student nearby assumes he is also interested in men. However, this is changed to a scarecrow in the localized text. Although he is known for being a womanizer, constantly chasing women, his ending with Felix leads us to classify him as Bisexual Implicit.
• Manuela: She has two same-sex paired endings with one mentioning love. Although it’s unclear if it’s romantic love, her ending with Dorothea may imply it, knowing that she does still flirt with Byleth regardless of gender, as mentioned in this thread. We have classified her as Bisexual Implicit.
• Abysskeeper and Mr. Backup: Although both are NPCs, their relationship has queer undertones (their full storyline can be seen here). Like other possibly queer relationships in the game however, their storyline ends with the Abysskeeper possibly marrying Mr. Backup’s sister. However, their relationship still implies their feelings for each other, so we have classified them as Bisexual Implicit. It is worth noting however that their storyline is only available in the DLC.

It is also worth noting at the time of writing this that not all Japanese supports have been translated to compare to how they were localized, so some queerness may be lost in translation. If you have evidence of this, please let us know by getting into contact with us.

LGBTQ references in this game series:

Fire Emblem: Thracia 776 (1999): Marty and Dagdar

Fire Emblem: The Blazing Blade (2003): Bramimond; Florina and Lyndis; Legault; Lucius and Raven

Fire Emblem: Sacred Stones (2004): Ephraim and Lyon; Joshua and Gerik

Fire Emblem: Path of Radiance (2005): Ike and Soren; Jill and Mist; Reyson and Tibarn; Sigrun and Tanith

Fire Emblem: Radiant Dawn (2007): Elincia and Lucia; Heather; Jill and Mist; Joke about Ike and Sothe; Kyza; Ranulf

Fire Emblem Awakening (2012): Gay Jokes and Queerness; Same-Sex Relationship Hack; The Hubba Tester

Fire Emblem Fates (2015): Forrest; Nina; Romance options; Same-Sex Relationship Hack; Skinshipping; Soleil; The Hubba Tester

Fire Emblem Echoes: Shadows of Valentia (2017): Leon; Lukas; Queer Readings

Fire Emblem Heroes (2017): Ally Support; Loki; Sharena

Fire Emblem: Three Houses (2019-2020): Byleth Pairings and Controversy; Non-Byleth Pairings

See also QRM’s entry for this game series

Citations:

1. Four-Loose-Screws. (2020, May 06). Ingrid / Sylvain C Support Translation. Retrieved from https://four-loose-screws.tumblr.com/post/617305972775452672/ingrid-sylvain-c-support-translation
2. GamingMayCry. (2019, September 20). Felix Goddess Tower Event – Fire Emblem Three Houses. Retrieved from https://www.youtube.com/watch?v=MJDVvrf5NYM
3. Justonegamr. (2019, July 28). Ferdinand & Hubert Support Conversations – Fire Emblem: Three Houses [Switch]. Retrieved from https://youtu.be/Wv20BDbZyxo?t=414
4. Noobsaigon. (n.d.). Fire Emblem Three Houses Endings. Retrieved from https://fe3h.noobsaigon.com/
5. StormwindGames. (2020, March 16). Fire Emblem: Three Houses – The Story of Abysskeeper and Mr. Backup. Retrieved from https://www.youtube.com/watch?v=h7ty2k3x1RI
6. Zoharemulator. (2019, July 30). So what’s Manuela like if you’re female Byleth? Retrieved June 17, 2020, from https://gamefaqs.gamespot.com/boards/204445-fire-emblem-three-houses/77903053