Knuxmerald

MasterKnux is the cargoship between Knuckles the Echidna and the Master Emerald from the Sonic the Hedgehog fandom.

Canon
In most canons, Knuckles is the guardian of the Master Emerald.

Sonic X
When Knuckles was transported away from Angel Island, while the Master Emerald remains there, Knuckles made it his mission to return home in order to reunite himself with the Emerald.

Sonic Mania Adventures
In "&amp; Knuckles", Knuckles was first seen carrying the Master Emerald in a forest within Angel Island. He then stopped to take a rest. Hearing a crash nearby, he thought of Dr. Eggman, the Heavy King, or Sonic attempting to steal the Emerald once again. Ray the Flying Squirrel landed beside the echidna and rolled around the Emerald. He greeted Knuckles and asks him where Mighty the Armadillo was. Knuckles shrugged, while Ray glanced and tried to touch the Emerald. Knuckles immediately held him and flung him to the sky. Later, Knuckles fought a trio of RhinoBots while Eggman stole the Emerald using the Tornado. Thinking Sonic was responsible for the theft, he chased after the biplane in anger.

In "Metal Mayhem", Knuckles charged through the lair and punched the already powering-up Metal Sonic, pushing both it and Eggman outside. The echidna then carried the Master Emerald out of the lair, unaware of the presence of Sonic, Tails, Ray, and Mighty nearby.

Fanon
Some fans tend to pair Knuckles with the Master Emerald instead of another character.

Fandom
DEVIANTART
 * Knuckles and Master Emerald on DeviantArt
 * KnucklesXMasterEmerald on DeviantArt