Nekodam

Nekodam is the slash ship between Nekomaru Nidai and Gundam Tanaka from the Danganronpa fandom.

Canon
In Chapter 4 of Danganronpa 2, the two both decide to do something after the starvation motive is introduced and the others are just waiting to die. Both agree to battle each other to death in order to sacrifice their lives to save the others from starvation.

Their friendly rivalry from the second game is referenced in the second episode of Despair Arc, where the two are playing one of Chiaki's video games together. Both continue attacking each other's character that causes their characters to fall off the platform and die.

In episode 9, the two stay behind during their class's search for their homeroom teacher, in order to fight the angry Reserve Course students who were about to attack Class 77-B.

They also share an event with Fuyuhiko in New Danganronpa V3's bonus mode, Ultimate Talent Development Plan, where Nekomaru tells them about their tactics for the upcoming sports festival, with Gundham and Fuyuhiko accepting it and having faith in Nekomaru's strategy.

Fanon
Although both have their more popular ships, with Gundham being involved in a love triangle situation while Nekomaru mostly trains with Akane, the ship escalated through their friendly rivalry.

However, the biggest reason for why they're shipped together comes from their murder case from Chapter 4 of Danganronpa 2, where they agreed to attempt to kill each other so that the others wouldn't die of starvation from the motive.

Fandom
AO3

Trivia

 * This is one of several ships between a victim and their killer, with the others being Leosaya, Chimondo, Yamaceles, Mahpeko, Tsumionji, Band Aid, Komanami, Nishichino, Amamatsu, Shiromami, Tojoshi, Shinnaga, Iruhara, and Oumota.
 * This is also one of three ships like that where both parties agreed to their roles, with the others being Toshi and Oumota.
 * This ship shares some similarities with Oumota, with Nekodam and Kaito both being the athletic hero type while Gundham and Kokichi are both pretending to be villains. As mentioned in the point above, both ships also agreed to orchestrate their respective murder cases.