Syaoran Li, Sakura Kinomoto, Tomoyo Daidouji, Eriol Hiragazawa, and Mokona Modoki are all in Card Captor Sakura and/or Tsubasa Reservoir Chronicles. I think it's rather obvious that I'm a big fan of CCS and TRC. Actually, I'm a big fan of (almost) all manga (but not all animes).
Syaoran and Sakura are a couple.
Eriol and Tomoyo are a couple.
Sakura and Tomoyo are cousins and best friends.
Syaoran and Eriol are cousins and are best friends (despite the fact that Eriol can annoy Syaoran very easily)
Mokona Modoki is a friend of everyone's.
Mokona is supposed to be a boy, but here, I decided Mokona woud be a girl.