RivaMika

RivaMika is the het ship between Levi and Mikasa Ackerman from the Attack on Titan fandom.

Canon
Levi and Mikasa are the two strongest soldiers of the Survey Corps. Mikasa eventually becomes a member of Levi's Special Operations Squad, handpicked by Levi himself.

Mikasa initially holds a grudge against Levi for beating Eren during the trial and talked about repaying him one day. She doesn't hesitate to blame him for Eren's kidnapping when they was chasing the Female Titan together. However, once Levi successfully retrieves Eren from the Female Titan and saves her from a certain death breaking his ankle in the process, Mikasa starts to take the responsibility over Levi's injury. She mimics Levi's technique when she takes down Annie in Stohess, and she generally becomes more responsible of her strength and thus a much more efficient soldier thanks to her encounter with Levi. Mikasa also starts to gain a deeper understanding of her captain and holds more respect and trust towards him through the course of the series. She is even shown asking Levi about his injury, and later she ends up defending Levi's leadership in front of her comrades, and lets Levi take care of Eren in the Reiss cavern while she was the one going for Historia. She still have no problems to call her captain out when he becomes to harsh, and he is quick to change his tone.

Levi for its part has always valued Mikasa's abilities. When he is unable to perform his duty he passes the responsibility of Eren's safety through Mikasa with full confidence in her, and later Mikasa is the one he trusts to kill humans. As a consequence, they have worked side by side several times through the series. Levi's only criticism towards Mikasa was her unwillingness to follow orders, he doesn't hesitate to call her out and he is quick to take a role of a mentor to her. Levi has also been speechless several times around Mikasa, it has been suggested that he is aware of the similarities between the two of them and perhaps that he sees pieces of him in her. He has generally display kindness towards Mikasa through the series.

It has been revealed that Levi and Mikasa are the last two members of the Ackerman clan, a bloodline of warriors who has served the royal family a long time ago but were persecuted to the brink of extinction after refusing to follow the First King ideology. They both are referred as by products of Titan science which can explain their share strength and exceptional abilities. Mikasa has discussed her past and the persecutions she was victim of with Levi and they have both tell the other about their awaking of power, but it has yet to be discovered if they have fully discussed their lineage or not.

Fanon
Rivamika popularity can be explained by the parallels that have been drawn between the two characters, their drastic relationships development that falls under the one-sided ennemies to friends trope, and the camaraderie that Mikasa and Levi have formed together through the series. Since they are the two most powerful characters who often team up together, they are referred in fanon as Humanity's Strongest Pair.

Because the two are the last member of the Ackerman clan, the ship has often been criticized for being incestuous. However, the incest argument has been debunked several times by official source. Levi and Mikasa come from two different branches of the Ackerman clan and thus are distantly related, they share a great-great-great grand parent at the closest. The Ackermans are not considered like a close family but rather like a bloodline.

Fandom
AO3

Trivia

 * http://canon-rivamika.tumblr.com/
 * http://levimikasa.tumblr.com/