ReiBert

ReiBert is the slash ship between Reiner Braun and Bertholdt Hoover from the Attack on Titan fandom.

Canon
Throughout their childhood in Marley, Bertholdt and Reiner trained together to become Marleyan warriors; they became quick friends due to Reiner's meek personality and Bertholdt's friendliness. They befriended Marcel and Annie Leonhart whom they were later assigned a mission with to destroy the Subjects of Ymir living within the walls and recapture the Founding Titan. Reiner and Bertholdt share two common goals: To return home and to bring glory to the shunned Eldians back in Marley.

After working together to breach a hole into the Wall Maria, they enrolled into the military and were placed in the 104th Training Corp. The two are almost always seen together as cadets, and were introduced together as partners. They are shown to be great friends and listen to Eren's story about his mother's death, although it's not obvious, Reiner was guilty about what happened and forced himself to believe that he was a soldier, Bertholdt is aware and is concerned for his friend's sanity. The guilt Reiner carried started affecting his grasp on reality, putting stress on his and Bertholdt's relationship. He developed a dissociative-identity disorder(split-personality), where his "Soldier" personality started taking over his "Warrior" one.

Despite Reiner's mental instability, Bertholdt continued to trust his judgement and follow him. The duo show great concern for each other and work well together. The Scouts shelter at Utgard Castle against the moonlight titans, Reiner nearly gets killed by one of the titans reaching into the window, but is saved by Bertholdt. They later work together to capture Eren and Ymir. After the Scouts manage to get Eren back, Reiner puts himself in a dangerous position by protecting Bertholdt with his titan's hands instead of fighting off the Scouts and mindless titans. Even without Eren, Reiner continues to protect Bertholdt as they gets swarmed by titans.

Before the Battle of Shiganshina District, Bertholdt is in his barrel and worried over Reiner. When Reiner is defeated by the Scouts and is left at death's doorstep, Bertholdt holds off Zeke's plan of bombing Shiganshina District with his titan transformation and chooses to save Reiner instead. This decision ended up having a fatal consequence for Bertholdt, who, because he failed to kill the Scouts sooner, ended up captured and eaten by Armin's mindless titan. His decision to put Reiner's survival above Zeke cost Bertholdt's his life and the mission's success.

Four years after Bertholdt's death, Reiner still thinks about him and the other fallen Marleyan Warriors. Reiner might be unaware that Bertholdt was devoured.

Fanon
In episode 29, Ymir and Reiner's conversation may imply that Reiner is gay/bisexual. As Ymir says to Reiner that he "didn't look like the type who would be interested in girls." This has caused a huge debate in the fandom whether Reiner is gay or not, and that if his relationship with Bertholdt may actually be deeper than just friends.

Despite Reiner's tough appearance and physical strength, he lacks a strong will and is actually the kindest of the Marleyan Warriors. On the surface, it looks like Reiner is constantly protecting Bertholdt who's timid and shy but it's the other way around. Bertholdt kept Reiner's grasp on reality from slipping and is there when Reiner's toughness gives out (Battle of Shiganshina District).

On AO3, ReiBert is the most written relationship for both Reiner and Bertolt. It is also the seventh most written relationship in the Attack on Titan tag.

Fandom
FAN FICTION
 * Bertolt/Reiner tag on FanFiction.Net
 * Bertolt/Reiner tag on FanFiction.Net

TUMBLR

Trivia

 * Reiner and Bertholdt share a character theme song, "Alternative Drive." It is sung by Bertholdt's voice actor, Tomahisa Hashizume and Reiner's, Yoshimasa Hosoya.