Shin Devilman

When Akira Fudou tries to save Ryou Asuka from being attacked by the demon Oysnas, they are both mysteriously teleported back in time. Once they pass through what Ryou identifies as a "Timeslip," the duo discovers that demons have been invading the past in an effort to tamper with major historical events. It is Akira and Ryou's job to stop the demons from corrupting key figures in human history before they alter the course of humanity.