Sonuckles

Sonuckles is the slash ship between Sonic the Hedgehog and Knuckles the Echidna from the Sonic the Hedgehog series.

Games
The two of them were initially enemies in Sonic the Hedgehog 3 due to Eggman's trickery, but after Knuckles realized the truth, he and Sonic came to have a more friendly relationship. Despite this, however, Knuckles still held an inhospitable attitude towards Sonic, due to their different points of view and natures.

Over time, Knuckles' relationship with Sonic has improved and he has come to see Sonic as both a rival and one of his best friends (the other being Tails) and help each other in many situations.

Sonic Boom
They are teammates, despite them being complete opposites as Knuckles' kindly personality to Sonic's snarky attitude. Knuckles considers Sonic his friend and is very loyal towards him. While though the two of them are always disagreeing each other, both still share a mutual bond of respect.

Overall, they are the truest of friends, referring to each others as "bros."

Fanon
Sonuckles has a neutral popularity, but it's not the most popular slash ship due to Sonadow's mainstream popularity in the fandom. In other words, Sonic Boom ' s Sonuckles gained some fan-following due to their brother-like relationship.

Tumblr

 * sonuckles tag on Tumblr
 * sonknux tag on Tumblr

AO3

 * Knuckles the Echidna/Sonic the Hedgehog tag on Archive of Our Own

deviantART

 * sonuckles tag on deviantART
 * sonknux tag on deviantART