Kamen Rider Ryuki: S1 E39 - A Dangerous Sign Kamen Rider Ryuki

Tiger betrays and easily defeats Alternative who had seemingly been his ally. Meanwhile, Ren has lost Eri, but upon hearing Yui is being targeted he is once again able to take action. Standing in his way is Professor Kagawa whose unshakable conviction that he must kill Yui leads to a clash with Ren.