When I was a little kid, I had only two official Sonic games. Everything else that I played was fangames.

In Sonic Smash Brothers (nostalgic game, RIP) I found out about Espio and Mighty. In introduction cutscene, they were seen together, so I thought that they were close friends. Well, they were in one team in Knuckles' Chaotix.

Later, I liked to play Sonic Scene Creator games, especially Amazing SSC v.2.0. There was a huge choice of game locations and characters, including Team Chaotix. They shared the same sprite sheet, so I found out that there's four members: Espio, Mighty, Vector and Charmy. The latter's sprite from Knuckles' Chaotix was as little as a chao, so I thought that Charmy was a passive member and followed one of the team members, just like Cheese follows Cream.

Much later, when I started buying games on PlayStation Network, I found an interesting game called Sonic Heroes. I puzzled: "Where the hell is Mighty? And wow, Charmy grown up bigger". After that, I read the sad story of Mighty. It turned out that he is a guest team member, just like Knuckles.

If Mighty still was in Sonic Heroes, he would be a paired character either with Espio (because he was almost as fast as Sonic) or Vector (because he has smashing power).