Shibuya Kazuya is the 17 year old president of SPR. He is sharp and extremely intelligent, but very much a narcissist...so he has been nicknamed by Mai "Naru" (Short for narcissist). Contrary to the other characters, he does not appear to possess any kind of spiritual power, and must count on his companions' abilities and his own intellect and knowledge to solve the cases they investigate. Though appearing cold and critical in front of his friends, he does care for them deeply and has earned their trust and respect. He and Mai apparently share a close relationship as she is the only girl he addresses by given name, unlike Masako, who becomes jealous of Mai as a result. (Source: Wikipedia)
He caused Psychokinesis (Poltergeist Effects), when he was little due to the huge amount of power he posses."Naru's power is in a league of it's own", as said by Lin once and so he taught Naru how to keep his power in check. It puts immense stress on Naru's body if he uses his power, enough to make him stop breathing.Major spoiler:
Eventually, it is revealed that Naru is actually the famed paranormal researcher and psychic, Oliver Davis, and that he has very strong psychokinetic abilities, which Masako Hara has witnessed. Although Naru has been taught how to manage his psychic abilities by Lin Koujo, it takes such a large toll on his body that the one time he does use it in the series, he collapses and is hospitalized afterwards. It is also revealed that Naru had a twin brother named Eugene (that Mai sees in her dreams as "dream Naru"), who originally helped Naru to control his abilities. They were nicknamed Gene and Noll; when Mai gives him the nickname Naru ('Na-ru'), he is taken aback because (in Japanese) it sounds similar to Noll ('No-ru'). Naru and his brother were orphans who were later adopted by the Davises, paranormal researchers in England. Naru learns that his brother has died, and using psychometry, is led to Japan. It is discovered that Gene was run over by a car driven by an unknown woman, and his body was thrown into a lake to destroy any evidence of the accident.