Journey Through the Psyche
Throughout the game, Sora expresses a variety of emotions; some obvious, some not so obvious. He generally maintains a positive attitude; however, just like any normal person, he holds some negative aspects as well. For starters, Sora doesn't always seem like he's the brightest crayon in the box; as noted by Riku, he tends to pick friends of the same caliber. Sora can also be rather impulsive and quick to anger, much like any normal 14 or 15 year-old boy. He quite often becomes frustrated with Donald’s comments, and is bit aggressive when something gets in his way. In addition, he can be rather rude and straightforward when confused as well. He also can speak out of line, not knowing where to place his respects. Although more thoroughly demonstrated through Roxas, Sora's capacity to hold anger is seen when he begins losing his memory of Kairi while ascending Castle Oblivion in Chain of Memories.
In some of art released by Nomura, Sora is displayed as expressionless and contemplative; it was different from his normal attitude and cheesy grin. When he first met Donald, along with Goofy, he wasn't exactly the happy-go-lucky Sora he's usually portrayed as; instead, he was rather upset. He was told that if he were to stay on the Gummi ship with them, he would need to smile more often.
"But you can't come along looking like that. Understand? No frowning. No sad face. Okay?"
-- Donald, Kingdom Hearts
There are several times within the series where Sora begins to lose faith in himself, just like normal human beings do. Although this particular emotion is more reoccurring in the first game, it continues on throughout the following one. For example, when Pooh loses his memory of Sora in Kingdom Hearts II, Sora becomes distressed when he doesn't remember his name. However, just as Pooh remembers it, he immediately forgets that the time when he forgot about it. Sora, a bit disgruntled that his endeavors to restore Pooh's memory were forgotten by Pooh himself, is noticed by Pooh to which he replies, "I like it ever so much when you're cheerful, Sora". Although Sora may occasionally falter when it comes to outwardly showing his greatest asset, he never fails to use it when it really counts, as seen after he and Riku defeat Ansem in the second game.
"Aw, c'mon, Riku. You've been hanging out in darkness too long. You gotta try and think positive!"
-- Sora, Kingdom Hearts II
It's this same optimism and good nature that contributes to his unselfishness; where most people are unwilling, Sora steps down to help even the smallest stranger in need. In the case of his foes, Sora has the capacity to find forgiveness in his heart, showing mercy and sometimes giving them the benefit of the doubt, such in the case with Maleficent and Ansem's Heartless (who was, unbenknowst to him, Riku in disguise). Regardless of how personally people may have wronged him, he tries his best to give them a second chance out of the goodness in his heart.