Sonuckles

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

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, helping each other in many situations. Since Sonic Heroes, the two have been members of Team Sonic along with Tails, although the three were already something of a team in Sonic Adventure 2.

Sonic the Hedgehog: The Movie
Sonic and Knuckles are best friends, with the echidna explicitly stating their relationship to the President while he tried to contact Sonic or Tails explaining the situation with Hyper Metal Sonic.

At one point, Sonic steps Knuckles on his head while fighting Hyper Metal Sonic. At the end of the film, Knuckles hits Sonic at the head as payback, with Sonic chasing the echidna demanding explanation.

Sonic Underground
In "Friend or Foe?", Sonic and his siblings Sonia and Manic, in their search for their mother, traveled to the Floating Island, being told by the oracle to "beware the echidna". They reached a sacred pool and unknowingly activated it. Knuckles confronted the trio and called them hedgehog thieves. Sonic said that he didn't expect a welcome like this, and replied that the hedgehogs are thieves in a way. Knuckles spun his arms, creating wind that pushed Sonic to a tree, then dug pit traps prepared for the hedgehogs. Sonia tried reasoning with Knuckles to no avail. After a short fight with Sonic, Knuckles activated the pit traps, pulling the hedgehogs down. Sonic escaped easily though, later he dodges Knuckles' attacks and allows himself to be chased by him. The chase ends near some rocky bridges on the island, in which Knuckles breaks one of them with the intent of Sonic falling down to earth, however with his super speed Sonic was able to catch up to him. The ground around Sonic began to shake, tipping Knuckles close to falling from the island's edge. After a quick banter, Knuckles fell off the edge, but Sonic saved him, who asked why would Sonic do that. Knuckles was tricked into thinking that the hedgehogs were his enemies, although he eventually found out the truth. Knowing that Sleet and Dingo would steal the island's Chaos Emerald, Knuckles activates a nearby pool confirming the duo's plan. Knuckles, Sonic, and his siblings were able to catch up to them. With their musical help, Knuckles was able to destroy as many Swatbots and drive the duo away while Sonic recovered the Chaos Emerald. Later that night, Knuckles treated the hedgehogs to krupnik and asked their purpose of coming to the island. When Manic replied that they were searching for their mother, Knuckles told them the fact that he has met their mother when he was young.

Following a long battle with Dr. Robotnik over the Chaos Emerald, Knuckles allows Sonic and his siblings to stay on the Floating Island if they ever need a break.

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

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

Sonic Mania Adventures
Despite not interacting with each other directly in the series, Knuckles blames Sonic for stealing the Master Emerald when Eggman used the Tornado. After Knuckles punches Metal out of the lair, the echidna calmly left with the Emerald, not paying attention to Sonic and his friends.

Sonic and the Secret Rings

 * In the world of the Arabian Nights, Sonic meets Knuckles's doppelgänger, Sinbad the Sailor when he came to save Sinbad from the pirates who captured him. While having no idea that Sinbad is the doppelgänger of Knuckles until after he comes across the caged sailor.
 * After Sonic and Shahra found away to free Sinbad from the cage, he tells Sonic how he can fight Ifrit. Even though the two did but heads with one another, until Ali Baba got them to stop glaring daggers at each other.
 * In the comic of Sonic and the Secret Rings, Sonic tells Shahra who he confused Sinbad for, along with sharing a few things about Knuckles.
 * At the end of the game, Sinbad aids Sonic on his next journey to find his way back to his home world, along with ensuring that the Erazor Djinn is never freed from his lamp again.

Sonic and the Black Knight

 * When Sonic encountered Knuckles's doppelgänger, Sir Gawain from the world of Camelot, the hedgehog comments that Sir Gawain is just like Knuckles.
 * After being defeated by Sonic, Gawain tries to attempt suicide for failing his King, but Sonic stops him from doing so.
 * To save Camelot from Merlina, Sonic give Gawain back his sacred sword, Galatine.

Fanon
Sonuckles has a neutral popularity, but it's not the most popular slash ship due to Sonadow's mainstream popularity in the fandom. However, the Sonic Boom version of Sonuckles did gain some fan-following due to Sonic and Knuckles's brother-like relationship in the show.

Fandom
FAN FICTION
 * Sonic/Knuckles (games) tag on FanFiction.Net
 * Sonic the Werehog/Knuckles on FanFiction.Net
 * Sonic/Knuckles (Sonic Boom) tag on FanFiction.Net
 * Sonic/Knuckles (Sonic Boom) tag on FanFiction.Net

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Trivia

 * When Sonic and Knuckles are paired up in Sonic Advance 3, the duo is known as Fighting Buddies. It is one of the four pairs with special names and the only one featuring Knuckles.

Variations

 * Sonuxadow - the polyship between Sonic, Knuckles, and Shadow the Hedgehog
 * Sonuxeam - the polyship between Sonic, Knuckles, and Cream the Rabbit
 * Sonuxouge - the polyship between Sonic, Knuckles, and Rouge the Bat
 * Team Sonic - the friendship including Miles "Tails" Prower