Meariri

Marika is the femslash ship between Mary Saotome and Ririka Momobami from the Kakegurui fandom.

Canon
During the presidential election, Ririka was looking for Mary Saotome, who she bumps into her (who bumps into who? It’s unclear with this phrasing and I can’t remember) and her mask falls off, in which she quickly puts it back on and then proceeds to take Mary with her. Once they're alone, only in the presence of Inaho Yamato, Ririka suggests a gamble. She puts one of her 100 votes in one of her closed hands and Mary has to guess which fist the chip is in. If she gets it right, she can keep the votes, but if she gets it wrong, she has to join Ririka in the presidential battle. And even if she wins, Ririka would simply follow Mary around.

Mary was against it and wanted to leave, until she heard about Yumeko Jabami being poisoned. Mary then ripped Ririka's mask off, saying that she can't trust someone who doesn't even show their face. She then questioned whether Ririka was ordered or wanted this herself. This left Ririka thinking. When Mary got a phone call that Yumeko was in trouble, she realized that Ririka organized the Nim Type Zero game, so that Mary would be forced to get the votes. Then Mary gripped one of her hands, opening the correct fist containing the chip.

Since then Ririka followed Mary around everywhere she went, wanting to fight alongside her. She also got more open towards Mary, taking the mask off for her. It seems like Ririka enjoys being around Mary, however, the feeling isn't mutual. Mary wants Ririka to start acting on her own and not just under the orders of her sister or someone else. Thus, Mary decides they should gamble. If Ririka wins, then she is allowed to accompany Mary during the fight. It seems that Ririka won off-screen, since she is still seen following Mary around. Mary still doesn't like her and gets annoyed at her.

Fanon
Even though this ship is not as popular as Yumary or Kirasaya, it has gained a lot of attention from the Western side of the fandom. For example, supporters of the ship like to interpret Ririka's affection for Mary as romantic, also bearing in mind that her twin sister (Sayaka Igarashi) is in a lesbian relationship with Kirari Monobami (Kirasaya) and having a similar sexuality is quite common among twins, especially when they’re  identical. Some also like to speculate that this ship has a chance of becoming canon or at least liked by manga author himself, as he tends to retweet fan art of it.

Fandom
FANFICTION

TUMBLR

Trivia

 * Ririka became Mary's fourth, more or less, close friend throughout the franchise. As a result, this ship also reflects this dynamic, being her 4th-5th ship as it emerges.
 * Fans, and it seems even the author himself, tend to view this pairings as a mirror or "sister," of KiriSaya. This is due to both ships including twin sisters with opposite dynamics. Unsurprisingly, Marika is the second ship, after Kirasaya, that he likes to retweet the fan art of.