Actually, in the movie he has a COMPLETELY different personality. He's nothing like he is in the book.

Plus what weapon he got depends on whether you're referring to the novel, the film, or the manga. In the novel, he got a knife. In the film, he got a paper fan. In the manga, he got a machine gun (if I remember right.)

But in the film, he joined the game for the fun of killing and shows a sadistic side that gets pleasure from killing. Kiriyama in the novel is nothing like that.