Fuyuhiko is initially incredibly stand-offish and rude to the other students on the island. He claims he's not going to play at being friends with anyone, and when he is questioned about this in Chapter 1, he states clearly that he would not hesitate to kill anyone of the others. He makes frequent references to his yakuza background and seems adamant at presenting this sort of "lone wolf" attitude. Fuyuhiko doesn't simply want to make friends but considers it not worth his time and beneath him. 

When Fuyuhiko does interact with the others (by choice or otherwise), his attitude is combative and irritable. He's easily angered, often threatening and/or insulting other people when they disagree with or complain about his actions.