May Contain Spoilers!

Riku Riku is Sora's best friend. They both live on the Island, and both have wanted to explore new worlds (Riku wanted this more so). Although they are close friends, they have developed a strong rivalry. Mainly it's just a friendly one though. However, when Riku is searching for Sora in Castle Oblivion, it's clear to see this rivalry has cleared up. By Chain of Memories, at the end, Riku follows the darkness in order to hopefully find Sora. He even goes into battle with Roxas twice, just to help wake Sora up. By the end of the second game, it's clear Riku has grown up considerably, and confirms his belief that no one could ever have a better friend than Sora.

Kairi Anyone who can't see their affection is probably just in love with Sora and wants his affection for themself. Kairi appeared on Destiny Islands suddenly, and has no memory of where she came from (Although it was later discovered to be Hollow Bastion, aka Radiant Garden). Sora, quite literally loves her enough to sacrifice himself for her. Kairi instantly recognises Sora as a heartless, and protects him from the other heartless surrounding them, bringing Sora back to life. When he finally meets up with her, he makes a promise to come back to her, and return the charm she gave him. Sora stops at nothing in order to fulfill his promise, and returns it to her at the end of Kingdom Hearts II.

Donald Donald has the same relationship to Sora as he does to everyone - Always arguing when a disagreement comes along. Donald cares about Sora though - We know this because of the way he wants to drag Sora back with them when Kingdom Hearts is closed. He also worries about Sora at times, but, being Donald Duck, hides it from everyone. He also doesn't like it being brought up that it was he who clobbered Sora when he was a heartless, as we saw by his reaction in Castle Oblivion. Like Goofy, he also tries to make Sora feel better when in despair (Even if at first he only cared about finding his own friend).

Goofy Goofy is close to Sora as well - He was the first one to go against the King's orders to be on Sora's side when Riku had the Keyblade! He's very reliable to Sora, and a very faithful friend. He may come across as a little slow, but Goofy's also a great team member who seems happy to be apart of the team. He also tries to prevent and stop arguements that break out between Sora & Donald, and worries about them when they do argue. When Goofy was knocked out by a boulder on his head, Sora showed great dispair over what at first was thought to be the loss of a good friend. He was extremely happy to welcome him back later.

Roxas Roxas is Sora's nobody, created when Sora transformed into a Heartless. Although the two have little interaction, Roxas had many dreams about Sora, and set off to find him. He appeared to be a bit jealous of Sora, after he was told 'nobodies shouldn't exist'. However, later, he battles Sora, to test him and see how powerful Sora really is, and possibly why the Organization feared him so much. Upon losing, Roxas smiles and leaves Sora with the words 'You make a good other half'. Although Sora can't see Roxas, either way, he is a part of him (as seen in later cutscenes), and Sora & Roxas seem happy about each other.

Naminé Naminé, under orders from Organization XIII, once badly tampered with Sora's memories. She replaced memories of Kairi with herself, led Sora deeper into Castle Oblivion with these fake memories. However, when the Organization members are taken down, Naminé explains to Sora why she did it, and also offers him a chance to regain his true memories - With the deal that both lose all their own memories of what happened in the Castle. Before Sora left to regain his memories, he made a promise with her, that he would never forget her, and that she would always be in his heart, no matter what happens.