Kazuya is another one of Tsukushi's childhood friends. He enrolls at Eitoku after his family comes into money through some real-estate deals. The other students at Eitoku draw a sharp distinction between Kazuya's "new money" and their "old money." The F4 in particular mention this difference fairly often. Tsukushi is both relieved to have a friend at Eitoku, and worried for Kazuya's safety if he continues to hang around her. She is particularly worried about Domyoji, who clearly considers Kazuya a romantic threat. Kazuya is fiercely loyal to and harbors romantic feelings for Tsukushi, but also relatively clueless and not very quick to pick up on things. He is not featured in the drama. (Source: Wikipedia)
