Usui is protective, stalkerish, slightly perverted, doesn't show much emotion, only cares about Misaki and what's best for her, quiet, mysterious, attractive, non-egotistical, good at everything, smart, cool.
His voice is slightly monotone and low for a teenage boy.
LIsten to the Japanese version for a reference: https://www.youtube.com/watch?v=VhOQmLs82e4
TO LEARN MORE ABOUT HIM:
"Usui, a silent but dangerous person, so mysterious yet only opened himself to Misaki. He is a very smart student, as well as being good at everything, and although very popular, he doesn't let it go to his head. Most of the time, he has a nonchalant and apathetic attitude but is always on the look-out for anything that may threaten or hurt Misaki, and he often saves her when she gets in trouble. He's 1st Rank beating Misaki to second place (much to Misaki's initial annoyance).
He doesn't think twice about rejecting a girl's confession, something he seems to experience often, and Misaki is also unhappy about this as she views it as him "harassing" girls. He can also survive even after jumping from the school roof without protective gear, just to save the photo that contains the secret of Misaki being a maid. He excels in playing chess, the violin, cooking, formal table etiquettes as well as most sports, much to many people's surprise.
Like most guys, he is awkward and not very good when it comes to expressing his feelings, so generally reverts to making perverted comments and references. The only times he expresses himself clearly are on several occasions when he confesses openly: "I love you, Ayuzawa" or when he expresses himself through actions such as kisses or tight hugs, which Misaki initially passes off as displays of bold sexual harassment.
It seems that Misaki is the first person that he developed feelings for. He often flirts and teases her(much to her annoyance). He usually stays around Misaki. He hates when people have dirty or perverted thoughts about her and gets very jealous when any other guy gets too close to her or draws her attention from him." - Fanpop.com (http://www.fanpop.com/clubs/usui-takumi/articles/212742/title/usui-takumis-personality#)
