Although often quiet and nervous around those who he doesn't know, Killua, when amongst tokota's that he is familiar with, has a great sense of humor and is extremely felicific, which means that he's prone to making others smile. He's optimistic and almost always sees the good in everything, no matter how bad the situation actually is. This causes others to view him as a dense individual, who doesn't realize that his actions have consequences. In reality, he's rather smart and loves to think about things.