Knuxsu didn't just happen, snap, like that. It all started in Knuckles the Echidna issue #4.

How Knuckles and Julie-Su met:
Here's how it happened. Vector the 鳄鱼 was in the pond 或者 lake 或者 type of body of water swimming when he sensed a threat and came to the surface to see a Dark Legionnaire. He thought it'd be real bright to attack the Legionnaire from behind (not his brightest idea). the Legionnaire quickly defeated him.

Later on that same 日 Knuckles was with his mentor, Archimedese, meditating and, of course, not focusing. The Dark Legionnaire came up from behind and attacked Knuckles....