ReiYumi

"He can be such a creep. No wonder he's single."

- Ymir about Reiner. ReiYumi is the friendship between Reiner Braun and Ymir from the Attack on Titan fandom.

Canon
Reiner and Ymir were initially enemies, as Ymir's Pure Titan attempted to grab Reiner and kill him, although Marcel Galliard got in the way. This left Reiner to think that his other friends were killed by her. When Ymir enrolls into the Training Corps, Reiner is unaware of Ymir's true self.

Their interactions start in the Clash of Titans arc, where Reiner checks on Ymir to see what she's doing in Castle Utgard. Ymir says that she's shocked, and claims that he seemed like the type of guy who wouldn't be into girls. Reiner retorts by saying that she doesn't seem to be into guys. Ymir grabs a can of herring and says that it should do. Reiner doesn't think anything of it, which leaves Ymir in shock, due to herring being a food from Marley, outside the Walls. There, she starts to learn about Reiner's true intentions. Reiner grabs the can and fakes not being able to read what is written on it, which is Eldian writing. Reiner too learns that Ymir is not the person she claims to be. Ymir glares at Reiner and their conversation is interrupted by Lynne reporting that Titans have started swarming the tower.

Squad Mike dies, and the only option left for the rest to live is for Ymir to reveal her secret. As she does, Reiner is in horror to see that her Titan is the one who ate Marcel. After the Scouts rescue everybody, Reiner transforms into the Armored Titan and captures Ymir. Despite being aware of Ymir killing Marcel, Reiner feels no hatred towards Ymir, and stays calm about the situation. Ymir is easily able to guess about Reiner's split personality, and calls it pathetic, to the point where Reiner tells her to shut up, and she quietly apologizes.

Ymir holds a lack of trust for him and refuses to go with his plan, until he mentions Historia, whom he knows how important she is to Ymir. Ymir then allows it, and is willing to leave. When she sees that the Scouts have arrived, she gets into an argument with Reiner, and says that she doesn't want to die. Reiner accepts, and waits for her to come with Historia.

While Ymir and Historia start escaping, Ymir notices that Reiner and Bertolt are surrounded by Titans, and are close to death. Ymir decides to save their life, and goes back to Marley with them. At Marley, Ymir writes a letter to Historia, while Reiner takes peeks at it, which Ymir thinks that it's no wonder he's still single. Even after her death, Reiner remembers Ymir and his promise to her, saying that they will save Historia and deliver her letter to her.

Years later, and as Reiner is fighting against the Nine Titans and is on the verge of death, Ymir saves him with her Titan, and he is greatly shocked to see this.

Quotes
"I'm way handsomer than her... probably!"

- Reiner about Ymir in the Junior High Manga.

Fanon
ReiYumi's friendship is extremely popular throughout the community, and ever since Ymir's teasing of him being into men, fans have seen their sort of rivalry as a "MLM and WLW hostility". Fanart sees them as love rivals, due to both being romantically interested in Historia, and mostly Ymir mocking Reiner for not being able to date her first.

Fandom
FAN FICTION

Trivia

 * Ymir has saved Reiner's life three times.
 * The first was by transforming into a titan and killing the titan horde that was attacking Reiner, Historia, Bertolt, and Connie.
 * The second was by yet again killing a group of titans attacking him.
 * The third was taking out one of the War Hammer titans who was beating him.