Takamura Suoh - Nokoru's relationship with Suoh is very deep and complicated (gosh that came out sounding so moronic!). Suoh is the one person who understands Nokoru the most. Suoh isn't blinded by Nokoru's charm, wealth, or skills. He sees beyond those things to the actual person and still finds the real Nokoru worthy. Because of this and Suoh's unflagging loyalty, it can be said that Suoh is Nokoru's first true friend (if you don't count that whole twisted thing with the Idomu kid). And Nokoru knows just how lucky he is to have Suoh by his side, and if Suoh's love for Nagisa weren't so obvious, I'd begin to suspect the beginnings of a yaoi type relationship between these two kids ^_~
Ijyuin Akira - Akira and Nokoru share a cheerfulness and enjoyment of life, and this gives the two of them a connection that Nokoru doesn't really share with Suoh. Both of them know how to have fun and are eager and willing to enjoy every moment to the fullest. In Akira, Nokoru has found a companion whose *genki* personality almost rivals his own. I can just see these two going out and partying together! However, it seems that when it comes to serious matter, Nokoru tends to rely more on Suoh than Akira. Akira also worships Nokoru, often viewing him with awe and fascination.
Yudaiji Idomu - I've said this before, and I'll continue to say it. The relationship between these two is very...shall we say twisted? How the kid came to blame Nokoru for stealing his mother's smile, I'll never know or come to understand. But it seems like Nokoru is one of the few people who managed to penetrate the barriers that Idomu set up around himself. Both of them became friends at a young age, and they have much in common. Idomu and Nokoru are from wealthy, influential families, and they share a bond that stems from having common backgrounds. This is probably what led them become friends so early on in life.
The Chairman - Even though it's not directly stated in the anime, it's pretty obvious that the woman who serves as director of the CLAMP School is Nokoru's mother. They carry the exact same fans and have similiar personality quirks - they adore setting up elaborate schemes to further their own ends and both love the CLAMP campus more than life. And even though we don't see much obvious affection between mother and son, it is clear that the Chairman has great faith in Nokoru's abilities (I think she says as much in one of the episodes).