Blue followed by Red. Sonic and Knuckles had been rivals for almost as long as they could remember even after Knuckles stopped working for Eggman they were still rivals through and through. It didn't matter what, they were competitive.
They were both heroes. But maybe it was Sonic's constant determination to win or Knuckles anger or jealousy that Sonic always got the credit. Maybe it was how they worked together that made them look like they had a rivalry. They were still friends after all.
Sonic would visit Knuckles a lot. The visits were always friendly but usually short. Sonic couldn't stand still for long. But as time passed the longer Sonic stayed. Coming the same amount of times but staying for longer. Soon enough he was staying there for days. Just him and Knuckles, that was it.
There was always tension between the two. Mostly positive friction but negative wasn't too uncommon between the two. The competitiveness between the two was extreme, only beaten by Sonic and Shadow's rivalry. That one was a lot more negative than this one though. This one was a lot more friendly.
During one of Sonic's visits they got close and kissed each other. Sonic immediately ran away while Knuckles looked to where he went. Knuckles was flabbergasted. But weirdly it felt nice. Knuckles missed Sonic as soon as the latter left the formers presence.
Sonic went back to Knuckles the next day and tried to apologize. Knuckles didn't mind though, so he brought Sonic in for a hug. At first Sonic was confused but slowly melted into Knuckles' arms and they stood there for just a little bit.