Sumibin

Sumibin is the non-binary ship between Robin and Sumia from the Fire Emblem fandom.

Canon
Robin is an amnesiac tactician and Sumia is the clumsy pegasus rider in training, member of the Shepherds, the guard of the kingdom of Ylisse. Robin and Sumia first meet  when he is accepted and introduced to the group, in the shepherds base. At that time, Sumia had a crush on their leader, prince Chrom, and when introcuding herself she trips and falls, making her ashamed.

The couple can be first paired when they go to Ferox in a diplomatic mission that goes wrong. Sumia that was left behind, then appears to save their leader, Chrom from being arrowed, and so Robin creates a strategy to divide themselves into pairs to win the battle against the Ferox soldiers.

From that day, they start to bond over their interest for books. Robin likes technical, non fiction stories while Sumia is more interested in romances and fantasy. She feels frustrated when when all of her suggested books don't catch Robin interest. Later, Robin reveals that he quite enjoyed the books suggested by her and they both lament when a good book comes to an end. Eventually Sumia confess that she likes to read and roleplay as fictional characters to escape reality, Robin finds it a bit weird but is ok with that, he tells her that she doesn't need to pretend to be someone else because she is perfect as she is though.

Sumia eventually realizes that her extreme escapism was not healthy. Robin confess that he couldn't stop to think on her and had fallen in love. He says that he is not the fairytale prince of her dreams but proposes to her. Sumia accepts by saying that by being together they can make their own book story. They marry and eventually have two daugthers, Cynthia and Morgan.

Robin discovers that he is actually son of Validar, the king of Plegia, a bordering kingdom that's enemy of Ylisse, and that he was raised to be the vessel of the dragon Grima, the dark deity that would bring the destruiton of the world. They can possibly find their time traveling daughter Cynthia who came back from the apocalyptic future, and also their  amnesiac younger daughter Morgan who just have memories of Robin but eventually she has lapses of her sister Cynthia and mother Sumia from the original future.

It's eventually revealed that Robin is the one that killed the exalt of Ylisse Chrom, and that Sumia also died in the war that happened after the assassinaton of the king. When Sumia was killed, her Pegasus made her way back to Cynthia, but it's not known how exactly she died, nor how was her life in the time period which Robin was possessed by Grima in the original timeline, the only information provided is that Sumia and Robin to some extent raised both daughters to the point of them having happy memories of their parents.

Fanon
It's the second most popular pairing for Sumia, and a fairly popular ship for Robin. The ship has a considerable amount of NSFW art, the most amount of art of the genre created for Sumia.

Robin and Sumia canonically marry each other only if Robin is male, since the option is not possible with female avatar. But the femslash version the ship also has a fair amount of followers in the fanon.

Fandom
FAN FICTION

Trivia

 * Robin is the only possible father that can give the hero class to Cynthia, that she wants so much.
 * In a cutscene when Robin is reminiscing the past and first time he met the shepherds, he reminds of the first time he met Sumia and laughs thinking on her.