Katsuhito walks up the stairs leading to the Masaki Shrine. When he gets to the top, he notices that there is no one there. He yells for Tenchi Masaki, his grandson, but there is no answer.

Tenchi is in the shrine office rummaging through drawers and boxes looking for something. The door opens and Tenchi sees no one there so he turns back around to continue looking. Katsuhito, his grandfather, has snuck up behind him and says "Curiosity killed the cat." Tenchi had been looking for some keys that his grandfather had on his person all along. His grandfather says that Tenchi can have the keys if he can get them from him. Tenchi tries and appears to fail (having his head stuck through a door). After his grandfather leaves, Tenchi turns around with the keys in his mouth.

Tenchi runs from the shrine and goes to a cave that has had heavy bars placed across the entrance. As Tenchi approaches the entrance he has a memory of his grandfather telling him about the legend of the demon and Yosho, the man that defeated the demon. It is said that Yosho's mystic sword guards the entrance to the cave and hold the demons captive. He also remembers his grandfather telling him that his name, Tenchi, means Heaven and Earth.

Inside the cave Tenchi sees a small replica of the shrine and inside is a sword stuck into the stone. He pulls the sword out and pulls the scabbard off to reveal a rusty blade. Thinking the sword a piece of junk, he swings it at a rock, cutting it in two and, at the same time, shattering the blade of the sword. This action causes a large stone to descend and an opening in the far wall to appear. Tenchi, like all good boys will do, investigates and falls down a slope to the bottom of the cave.

There is a pit in the center of the cave and, as Tenchi looks into it, he notices a mummified body. He gets frightened and drops the sword hilt. As he picks the sword up, the mummy's hand reaches up and grabs him. It places a hand on his face and pulls him close until a flash of light knocks Tenchi away from the mummy and toward the entranceway. Tenchi turns and clambers back up the slope and into the main portion of the cave. He grabs some creeper and ties the stone that he had cut in two back together. The opening in the wall closes and Tenchi makes his escape.

Unknown to Tenchi, a tree in the middle of the lake starts to send out beams of light toward space.

It is unknown how much time passes but Tenchi is now back at home and has returned to school. A friend of his asks how his vacation was and they have a conversation about girls and Tenchi's lack of getting to see any. The friend insinuates that Tenchi may have slept with older women and Tenchi knocks him into some lockers. Tenchi then runs to the roof of the building and falls asleep. He dreams about the mummy in the cave and ends up sleeping until night has fallen.

When he wakes up, he notices a cat that runs up to him and then disappears. He then hears a bell tinkling and turns to see a woman sitting on the roof. The woman's eyes glow golden as the mummy's eyes in the cave did and she begins to chase him around the roof trying to kill him. It is later revealed that her name is Ryoko. She seems to be playing with him like a cat does its prey. He finally escapes down the stairs and into the school where he hides in an office. He hears Ryoko walk by and breathes a little easier until he notices the smell of gas. He leaves the office and goes to the science room where the gas is coming from.

Ryoko materializes through the wall and has Tenchi cornered. Tenchi has visions of the headlines of the next day's newspapers about his death when he comes up with a brilliant plan for escape. He yells, "Hey, what's that outside the window." Ryoko, to Tenchi's surprise, falls for it and turns to look. Tenchi makes his get away. When Ryoko turns back and notices Tenchi gone, she gets mad and flares up her energy sword causing sparks. These sparks ignite the gas and the room blows up. Tenchi is somewhat relieved that she is gone but also notices to himself that she wasn't bad looking either, when she walks through the flames and comes after him again. He ducks into a stairwell and is saved by a mirror that attracts Ryoko's attention. She just can't stand the sight of herself looking all dirty and ragged.

Tenchi goes down the stairs to his school room and gets his bag that has the sword hilt in it. It's at this point that he realizes Ryoko is using three gems, two on her wrists and one on her neck, for power. He decides that all he needs to do is get those gems and he will beat her. Ryoko, in the meantime, has floated outside the school and finds Tenchi through the windows. She blows up the room he is in and Tenchi narrowly escapes. In the schoolyard he meets Ryoko and she advances on him with her energy sword. She swings on him and he holds up his school bag in defense. The sword hilt in his bag deflects the blow and begins to glow. Ryoko throws a couple of energy balls at Tenchi but these too are deflected. Tenchi then attacks Ryoko with the sword that has been energized somehow into a light blade. He says that the blade seems to be fighting by itself and he succeeds in cutting off Ryoko's hand. The gem falls to the ground explodes and Ryoko concedes defeat. She then sinks into the ground.

Tenchi decides that he had better get out of there before the police and fire departments get there to blame him for all the mess. When he gets home he goes to his room and sits on the bed. He looks at the sword in wonder for a while and then lies back on his bed. When he does this, he notices that someone is in his bed. He pulls back the covers to reveal Ryoko.