Asheleth

Asheleth is the non-binary ship between Byleth Eisner and Ashe Ubert from the Fire Emblem fandom.

Canon
Byleth meets Ashe at the Officers Academy at Garreg Mach Monastery, if he/she picks the Blue Lions House, Ashe will instantly be his/her student. However if Byleth chooses the Black Eagles House or the Golden Deer House, then Byleth can still recruit him, before the 5 year time-skip. If Byleth is a male, then there would be no romantic tension between the two. However if Byleth is female, then, they can marry, before the final boss, if the player gets A level support with Ashe, Byleth will visit her father's grave and take out the ring that he gave her, his words will echo, of her father telling her to give the ring to a someone that she loves as much as Jeralt loved his wife, if the player chooses Ashe, then after the final boss, they will get married.

Azure Moon
If the player/Byleth chooses the Blue Lions house, he/she will be introduced to Ashe as one of his/her first students. After the timeskip they reunite along the other Blue Lions at the monastery. They will fight together for the kingdom. After the war Ashe is formally appointed the new head of House Gaspard and Byleth becomes the new Archbishop. If Byleth achieves an S support with him, he will join her as knight and aide, and then marrying. Whenever thanked for his political contributions, Ashe will always give credit to his wife.

Crimson Flower
If Ashe wasn't recruited before the timeskip he will fight against the Adrestrian Empire and the player during the route's final boss fight. If Byleth battles him, he tells him/her to not look at him, for doing so will throw off his aim. Killing him is not required to win the fight.

If he was recruited before the timeskip, Sylvain will join the war against the Church of Seiros to learn the truth about his adoptive older brother and father's deaths. After the war, he is formally appointed the new head of House Gaspard. If Byleth marries him, she will help him to heal the world from the damage done by Those who Slither in the Dark; their adventures inspiring folktales.

Verdant Wind/Silver Snow
Regardless if Ashe is recruited before the timeskip or not, he will leave the player and face them at Ailell as an optional foe. However, if he was recruited pre-timeskip, Byleth has the option to spare him and allow him back into the party upon defeating him. After the war Ashe is formally appointed the new head of House Gaspard and Byleth becomes queen of the United Kingdom of Fódlan. If Byleth achieves an S support with him, he will join her as knight and aide, and then marrying. Whenever thanked for his political contributions, Ashe will always give credit to his wife.

Fanon
The most popular version of this ship is the variant with female Byleth. This pairing is quite popular since Ashe is available in all routes; however, it does face competition from other Blue Lions ships like Dimileth and Sylvleth.

Fandom
Ashe/Byleth tag on AO3

Quotes

 * "I genuinely enjoy helping people. It's a great feeling, making someone smile. So if there's anything I can do for you, I want to do it. Because I care about you." - Ashe to Byleth
 * Confession:
 * Ashe: "Yes! Sorry, I'm...I'm struggling for the right words. It's funny. I've rehearsed this so many times. But when the moment actually came, it all just ran right out of my head. What I mean to say is... I love you and I want to marry you."
 * Byleth: "I feel the same way."

Trivia

 * One of Byleth's nicknames is the Ashen Demon. This could be taken as a sign that they were meant to be.