Oumiki

Oumiki is the het ship between Kokichi Oma and Mikan Tsumiki from the Danganronpa fandom.

Canon
Mikan and Kokichi are from different games, and thus do not meet, but they share an interaction in the Ultimate Talent Development Plan bonus mode. In it, Mikan is charged with treating the injured students for the sports festival. Kokichi takes advantage of the beds, and fakes an injury to get out of them. Mikan inquires if he's faking, to which Kokichi admits, then seems sad about it. Mikan cries and apologizes for figuring it out, begging him to not hate her. Kokichi then gets out of the bed, and says that he knew that she would figure it out.

The characters also share many similarities. Mikan and Kokichi both have very innocent appearances, that make them seem very kind hearted. While for Mikan, it is mostly true, but she does have some sociopathic tendencies as a result of her implied abuse. Kokichi however is very cunning, and uses his appearance to seem like a young child, to add to his lies. Kokichi is also commonly believed to have been abused.

They are extremely different in one regard though. Mikan has a very submissive personality and is very clumsy. She constantly believes that she is hated, and that being abused is better than being ignored. Meanwhile, Kokichi loves attention, but likes to steal the show, instead of being bullied for it. He is very dominant personality, and a compulsive liar.

Fanon
Oumiki is considered a rare-pair within the fandom, because the two characters are from different games, and the commonly held belief that Kokichi is gay. However, proponents of the ship will imagine Kokichi helping Mikan overcome her trauma, and become able to stand her ground. The ship's main rivals are Saiouma and Oumeno for Kokichi, and Band Aid and Hinamiki for Mikan.

Other people interpret this as a family-ship instead, possibly due to their similar appearances, and refer to them as parent-and-child or siblings. For parent-and-child connections, the most common one makes Mikan the mother, and Nagito Komaeda the father. This connection ships Komamiki by definition, and also makes Oumaeda a father-son family-ship. This could justify parts of Kokichi's personality, such as his greater-good philosophy, which could have been instilled in him by his fan-father. However, Nagito is also commonly believed to be gay, making this a controversial pick.

For those people who interpret Oumiki as siblings, they typically headcanon them as very different, almost a Yin and Yang pair.

AO3
Ouma Kokichi/Tsumiki Mikan tag