No Need for Monsters! - S1.E4

Ryoko becomes a bit too curious about a mysterious cave near the Masaki shrine, and despite warnings of a legendary demon that sleeps within, she ventures inside dragging the unwilling Tenchi with her. They accidentally wake the demon and are chased from the cave. However, the "demon" turns out to be Washu, a mad scientist genius who was expelled from her academy 700 years previously.