EreRei

EreRei is the slash ship between Eren Jaeger and Reiner Braun from the Attack on Titan fandom.

Canon
The two had a pretty close relationship with each other before Reiner and Bertholdt revealed to be the Armored and the Colossal Titan. It was said Reiner was a big brother to all the cadets and was the person Eren admired the most as a teenager. They foil each other throughout the series, becoming character counterparts - something Eren lampshades when they are adults.

Training Cadets
Following Eren’s first impressions of the trainee life, he went from bragging about killing titans to perceive that becoming a skilled soldier wasn't an easy path. His frustration is clear not only about feeling ashamed about not understanding the basics of vertical maneuvering but that it would mean not being able to be on the frontlines to fulfill his concrete desire to exterminate the organisms he hated so much. He dismisses Mikasa’s and Armin’s attempts to cool him down (Mikasa suggests he could just be a technician to contribute and not to worry about loneliness because she would leave the camp to stay with him anywhere and Armin tries to stick to the possibilities of why he couldn’t stay still with the gear). Finally, Eren hears Marco’s advice to ask for help from other skilled cadets - Reiner and Bertholdt. They have a proper moment to meet each other and Eren, Armin, Reiner, and Bertholdt talk about their past experiences discussing the terror of the titans, and the oldest duo question Eren and Armin on why they still want to be part of the army. The first parallel between Reiner and Eren is made explicit when they exchange similar determination gazes while spelling their mains goals (for one, be able to return home, for the other, kill all titans). Reiner seemed to approve of Eren's determination and decided to help him. It seemed that Reiner meant to help Eren genuinely, constantly partnering the younger on training exercises. During the three years of being a cadet, Eren built his concept of a soldier code by the influence of Reiner's words. His philosophy of "always moving forward" marks Eren's perception of life in general, becoming a shared motto later. It's noticeable that Eren was called by his father as an antisocial kid that had only Armin as a friend before Mikasa came to live with them, so knowing how much time Eren spent with Reiner and listened to him has a different weight after Reiner's betrayal.

Clash of Titans
When Eren is on top of the Wall recovering from Castle Utgard's ordeal, he questions Ymir's condition and gives Reiner a hand up the Wall as Historia explains her true parentage. Helping Armin up as well, Eren goes to check on Reiner after hearing about how bad his arm was injured in the Castle; this, along with the moment that Reiner was almost killed by the Female Titan, causes Reiner to comment that he doesn’t expect that he'll live much longer and that they should keep fighting until the breach in Wall Maria is covered. After Bertholdt tells Reiner that they won't have to wait much longer and can return home soon, Hannes arrives with news. As Hange orders them to stay on standby in Trost District, Reiner goes to speak with Eren in private. Reiner reveals himself as the Armored and reveals Bertholdt as the Colossal Titan. He then respectively tells Eren that they won’t attack the Walls if Eren returns to their homeland with them. Eren recalls Hange's theory about how Reiner and Bertholdt might be accomplices to Annie and tries to persuade Reiner that he's just tired and not thinking straight. In response to Eren's disbelief, Reiner removes the bandage on his arm and reveals that the wounds he had were regenerating. Mikasa attempts to protect Eren but Reiner and Bertholdt transform into their Titan forms and attack. Reiner grabs Eren while Bertholdt kidnaps Ymir and Eren, disgusted by his former friends, transforms himself.

Eren started to despise Reiner after he revealed himself as the Armored Titan. He started to only view Reiner as a despicable traitor to humanity you had no right at all to live. Eren wanted to make sure that he killed both Reiner and Bertholdt with the slowest gruesome pain they would ever feel. He felt that that would be the only death suited for disgusting traitors like them. Reiner discovered at the ending of the arc that Eren owned the Coordinate and realized how bad that was giving knowing very well how Eren was as much or more determinate than him.

After learning a bit more about his past, about the nature of titans, some secrets of the Walls, and what his father had done to inherit the Founder Titan, Eren's understanding of the world grew and so his hatred for Reiner changed to a rather fated-to-kill duty, highlighted by answering to Historia's question with "I must kill them". She asks if he wants to, to what his downcast to repeat only "I have to." Later, Eren plays a part in the Survey Corps strategy to take back Wall Maria and reach his father's basement by setting combat with the enemy in Shiganshina. Eren and Reiner fight each other again, now more on a strategic spectrum of the combat rather than out of their unsolved tension. For Eren, as for other cadets like Jean, Sasha, and Connie, having to kill Reiner felt like an empty task that had no other option.

Marley Arc
A time skip of four years follows, turning the point of view to adult Reiner and his life in Marley. Some of his flashbacks focus on Eren of all people, one of them right before actual Reiner attempts against his life (being interrupted by Falco's outside complaining in real-world). When Reiner eventually talks or remembers the old times in Paradis with the 104th cadets, it's a mix of longing, regret, and sadness.

When Eren and Reiner meet again four years later, Eren's hatred towards Reiner seems to have gone down to some point, expressing to Reiner that it is good that he had managed to return to his hometown. In return, Reiner was shocked by Eren's return to him and could barely say a word to him. Eren expresses sympathy towards Reiner after learning the truth about Reiner's mission within the Walls and the world's hatred towards Eldians and experiencing the same infiltration mission within Marley that Reiner carried out years before. Eren admits he and Reiner are the same, driven by freedom for their people and manipulated by corrupt leaders for the actions of their ancestors. Eren even admits his own anger towards Reiner and Bertolt was a bit too much due to him not knowing their reasons why. Eren looks pained but genuinely concerned about Reiner, sincerely just looking for an answer to his inner conflictual question. Thanks to Reiner's response, Eren states that they are the same, as two sides of a coin.

Eren starts a raid in Liberio, saying that he will "keep moving forward". Despite not being interested in killing Reiner, Eren has his agenda of destruction clear and Willy Tybur declares war on Paradis Island. Later on, Reiner is urged by Falco and Gabi to take part in the titan battle in order to rescue the Jaw Titan from being consumed by Eren, that curiously seemed to forget the matter at hand to run for a new match with his long-term arch-enemy of sorts. As Reiner showed no big resistance, Eren retreats, giving one last sad glance at Reiner while promising to see him again soon.

Motivated to rescue Gabi and Falco, Reiner proposes that Marley delivers a surprise attack on Paradis one month after the assault in Liberio, showing up for a new titan duel with Eren. Instead of keeping true to his stoic and calculating demeanor, Eren ran straight to call Reiner for a fight, engaging in a chaotic match with him and Porco, aside from enemy troops. Reiner internally monologues about how they are not that similar and admits that Eren had suffered enough much like him and everyone else. The match is interrupted by Falco's titanization and attempt to consume Reiner, but then going after Porco instead - this all part of Zeke's strategy to lure the enemies while Eren could run for his older brother.

During the Rumbling, Reiner eventually theorizes that Eren wanted the few people that had some titan-related powers yet to keep their skills in order to stop Eren's global attack. It also comes with Reiner's realization of what Eren meant by saying they were the same.

Attack on Titan Junior High
Played for laughs, Reiner acts as a "cursed princess" for a school drama, in which the curse could only be broken by titan slaying and a kiss from the Prince - Eren. This makes Eren very nervous due to a "spitphobia", while general comedic chaos leads to Frieda taking the role of the Prince while Eren suffers a usurping attempt from Jean. After learning from Eren that Reiner is the princess to be kissed, Jean is stunned by Eren's professionalism, as the boy gives a motivational speech about overcoming his spitphobia to let Reiner's tongue come in.

Spoof On Titan
Also played for laughs, as Eren is even more oblivious to love than the canon series self, he seems to not get why all the boys talk about Mikasa's great points. All Eren can relate was the deep admiration towards her muscle strength, giving his two cents about and adding that Reiner was quite as incredible as her. Poor Reiner is totally taken aback by the sudden "love confession".

Fanon Portrayal
Fans who view their relationship as platonic usually put Reiner in a 'big brother' role. Many fans like to point out how Eren and Reiner's characters are foils of each other, especially after the time skip.

On AO3, the ship has over 900 fanfics. The most common portrayals that follow the canon setting put Eren as the hot-head teen with a huge crush on Reiner while Reiner feels a bit conflicted to have feelings for someone with "devil blood" for their time as cadets. Works focusing on their reunion as adults in Marley varies from an angst longing to very dysfunctional loving sessions. Alternative Universes also are very common to explore their romantic relationships in healthier environments, such as married couples with different jobs or high schoolers, especially based on Plain Jane Eren and Jock Reiner from High School Castes AU on the manga fake previews. However, largely due to the latest season of the animation, some AUs portray them (comedically or not) in a dysfunctional romance, commonly putting Eren as a stalker or a very possessive type of lover. The artist Columbo popularized this sort of interpretation in a modern AU, wherein Eren is portrayed as a "toxic ex" and Reiner's emotionally sensitive side is exaggerated.

A Slap on Titan
No intentional romance was plotted in the YouTube parody by Tom Andre, but the high popularity of the series' take on Reiner's character and the over-the-top bromance with Eren were acknowledged by many shippers especially in the Western fandom, quoting Reiner's favorite crayon colors, his general no pain no gain satirical advice and the mysterious concept of "Pound Town". Reiner also is stunned at Eren's titan form, which holds a gym's goal shape, often referring to Eren as "Jägermeister". As the parody only covers episodes from the first two seasons of the animation series, a lot of fanworks build the parody versions of Reiner and Bertholdt's reveal to Eren over the Wall Rose and Eren and Reiner meeting after the time skip based on their characterization from A Slap on Titan.

Fandom
FAN FICTION
 * Eren/Reiner tag on FanFiction.net
 * Eren/Reiner tag on FanFiction.net
 * Eren/Reiner tag on FanFiction.net

FAN ART

POSTYPE
 * 에레라이 tag on POSTYPE

TWITTER

TUMBLR

Trivia

 * In an interview, Hajime Isayama stated that no woman among the 104th cadets would be fit for Eren, but, regardless of gender, the characters that would suit Eren the best would be either Marco or Reiner. It matches the amount of admiration Eren felt towards Reiner.
 * Eren firstly vows to exterminate the titans when he was 10 while glaring at the Armored Titan, then he vows it again in the face of that very titan's host, three years later. Reiner's reaction? Instant admiration.
 * Parallels and Call-Backs: many, many of them - a twitter user made a long thread comparing panels and similar lines throughout 137 chapters:
 * Eren and Reiner foil each other as the hard-working determinator kids from their respective trio of close friends.
 * Both boys weren't supposed to inherit their respective titan powers, as they aren't naturally gifted or talented.
 * They suffer from hero-wannabe chronic disease and cumulated survivor guilt.
 * Despite all obstacles and keep failing, both of them refuse to give up before change anything.
 * During Uprising Arc, Hange proposes a series of experiments on Eren's Attack Titan to test its limits and powers. During Marley Arc, elements from the Warrior Program's files indicate that Reiner endured painful tests to measure his Armored Titan's endurance.
 * Facing their fails and flaws, Eren and Reiner measure their value only if they can be useful for whatever greater good they believe.
 * In Chapter 74, Eren is not yet transformed into his titan while standing above the Wall Maria, staring menacingly at Armored Titan on the ground before their match. In Chapter 116, their positions change, with Reiner looking down at Eren from a zeppelin.
 * In Chapter 94, the panels of kid Reiner beside Bertholdt walking next to the huge wall that isolates Liberio ghetto while making his whishes to the sky follows a twin pair of panels of kid Eren sitting by the grass, shadowed by the Wall Maria, making wishes to the sky while Armin is calling for him with a book in his hands.
 * In Chapter 16, Eren helps Reiner to get up after a training exercise by offering his hand. In chapter 42, Eren helps Reiner to climb up the Wall Rose by offering a hand. In Chapter 97, Reiner recalls himself on a flashback offering a hand to help Eren to get up after an ODM training fall. In Chapter 100, Eren offers a hand to help Reiner to get up, triggering his titan shifting.
 * In a flashback on chapter 97, Reiner cheers up a very frustrated Eren to "move forward" (as seen in one of the quotes above). In Chapter 100, Eren helps Reiner to get up while expressing his will to "always keep moving forward", which became one of his mottos.
 * In a similar fashion, Eren recognized Reiner had suffered all the time being when they met at the basement. While fighting Eren in their titan forms, Reiner recognizes that Eren also had suffered enough.
 * A strong-willed boy that lived his childhood in a city isolated by walls has one main goal in mind and pushes himself to reach said goal. He is sheer determination when he lacks natural talent, noticeable intelligence, or any other remarkable skill like the other kids hanging around him. Then, he decides to follow a military program for his selfish desires. As a teenager, he is an outspoken passionate dude of his hometown trio (that has a sensible smart dude and a stoic strong girl). Reiner or Eren? The answer is yes.