2x15 - Kamen Rider

The daughter of Dr. Okajima, an atomic physicist who escaped the clutches of Destron with the help of the Double Riders, saves the badly injured Kazami Shiro from the basin of a waterfall. She is then stalked by Burner-Bat, who is looking for V3. With the help of Dr. Okajima, Shiro is able to find the memento from the Double Riders, which holds the secret to V3's four weaknesses. What are they?