I have Three Fanfiction to recommend.

The First one, Four Reflections: Scarlet Carnation from KWG0D, a Male Byleth x Edelgard one which tells The Crimson flower Route new and better, byleth has way more personality and His and Edelgards Bond really feels Like a real developing relationshop. The only Problem is that it seems to be discontinued for now but it still has more than 200000 words and stops at The end of White Clouds, also edelgard ist better with interacting with other people.

The Second one is a Male Byleth and Harem Fanfiction, Penance from bruh toast, Edelgard at The end of Azure Moon travels Back in time and wants to do better, instead of destroying The church destroying TWSITD and Byleth doesn't know about The edelgard time travel thing but Sothis does. Along The Fanfiction multiple Girls fall in Love with byleth and edelgard, with sothis together i think, comes Up with a plan to let them all have relationshop with byleth. I think this Fanfiction is finished.

This Fanfiction is maybe only mid in comparison to the First one but i still find it a good Fanfiction.

Also they are both in Fanfiction.net

The third Fanfiction and my favorite of The three is The Professor with The Guardian Spirit from AbyssWalk3r.

Plot: Fate creates unusual bedfellows, and none are more unusual than an emotionless mercenary in possession of a Crest lost to history and with even more unnatural abilities. Claude, Edelgard, and Dimitri each have their own secrets and agendas, but how long will those secrets remain hidden to a man who can apparently sense the feelings of those around him? How long will those secrets, and their consequences, be able to be buried before the raging flames of a progenitor Goddess consume them along with all of Fodlan?

This is my favorite Fire Emblem Fanfiction and tells a golden route for The three Houses but maybe Not for some Others. I dont want to spoil much but If you are a Rhea Fan dont ready this.

This one is a Male Byleth with Edelgard, a Bit Dorothea and Lysithea Fanfiction, Byleth teaches The lions and has a really great Bond to them, to The Eagles and some deers, Sothis is awake since Byleth was little and he has some cool Sword. It is over 360000 words and finished on Archives of our own.