Prediction
In all likelihood, Subaru wants to kill Seishirou. Seishirou had killed Subaru's beloved sister, Hokuto, as well as the illusion of Seishirou whom Subaru had fallen in love with. Subaru knows it was only a fa�ade, a trick; he's no fool. And what would that acknowledgement do to him? He is betrayed and has lost everything that he loved and could have lived for. He no longer has a motive to live. Yet, he cannot kill himself. (See X 11 for details.) He is an empty husk of a person who is forced to live in the same world as the killer of his life; Seishirou.