The girls have been assigned to help with cleaning the shrine, but whilst Ayeka is willing to work hard, Ryoko prefers to slack off, and Mihoshi soon claims to be too hungry to help any further. Worse still, Ayeka’s claim that helping out is the least she can do only land her with more work when Katsuhito suggests she wipes the floors as well as sweeping outside.
Fortunately for Ayeka, she soon gets a well-earned break when Sasami comes over to say that lunch is ready. Hearing this, everyone is eager to return to the house, including Ryo-Ohki, who comes bounding out of a nearby cave.
As Katsuhito explains, this particular cave is the actual Masaki shrine; according to legend, a goblin was sealed inside the shrine seven hundred years ago, and because of that, the place is best left alone. Ayeka and Mihoshi are all too willing to listen to Katsuhito’s advice, but Ryoko and Sasami are curious to see if a goblin really is inside. Worried, Ayeka quickly talks Sasami out of going, and Ryoko decides to give it a miss too- at least, until she can find someone willing to accompany her.
Walking home from school later that evening, Tenchi only wants to get back to the house, but Ryoko has other ideas for him. Appearing behind him, she pulls out a rope, and whilst a nervous Tenchi tries to figure out what she has planned, she quickly ties him up, causing him to drop his school satchel. Tenchi is coming with her to the shrine, whether he likes it or not.
Whilst Ryoko drags a reluctant Tenchi into the depths of the cave, Ryo-Ohki goes out looking for him, only to discover his satchel in the woods. Back home, the girls are already worried about why Tenchi is so late, and when Ryo-Ohki drags the satchel in, their fears only increase. Desperate to know where Tenchi is, Ayeka begins shaking Ryo-Ohki and asking her to explain- but unfortunately for Ayeka, the only one who can understand Ryo-Ohki is Ryoko.
Suddenly realising that Ryoko is also absent, Ayeka begins to worry that she and Tenchi are off on a date together. After being bribed with carrots, Ryo-Ohki is willing to forget Ayeka’s earlier treatment of her, and agrees to help track down Tenchi and Ryoko.
Meanwhile, Tenchi and Ryoko have reached the back of the cave, but Ryoko isn’t willing to go home just yet. Blasting away the back wall, she reveals a passageway leading deeper inside, and is quick to bravely push Tenchi down the passageway in front of her. Taking a step forward, Tenchi steps on a floor stone and triggers a trap. Something comes flying out of the passageway, and whilst Tenchi quickly dodges, Ryoko is hit full in the face!
Ryoko appears to have struck by an arrow, but when Tenchi begins to say a eulogy for his fallen companion, she gets up and pulls the arrow off her face- it was only tipped with a suction cup. The arrow also has a message attached- “go home, you fool.” Fed up, Ryoko decides to leave, but as they turn to go, Tenchi hits his head on a rock, triggering another trap.
This next trap brings down a portcullis, confining Ryoko in the back of the cave, whilst a sign labelled ‘stupid’ drops down in front. Angry at being mocked, Ryoko destroys the portcullis and starts searching for her tormentor, but only succeeds in triggering more traps. Soon, Ryoko is fighting off spiked balls, giant logs and throwing stars, whilst poor Tenchi gets dragged along behind.
The other girls have finally reached the entrance to the cave, and this time, Ayeka is not afraid to go in- separating Ryoko from Tenchi is much more important than any legendary goblin.
Whilst the others make their way into the cave, Ryoko finally smashes through the booby traps and into an open chamber at the very back of the cave. A mysterious crystalline meteorite sits in the centre of the chamber, and, whilst Tenchi watches as it begins to glow inside Ryoko is quick to seal off the exit with a large rock. When Tenchi suggests going back, she tells him that they should stay- this is the perfect place for them to be alone for a while.
Tenchi tries to look away while Ryoko begins to undress, but with the rope still tying him around the waist, he cannot move too far away. Fortunately for him, the others have reached the back of the cave, and they quickly burst through the wall. Storming in, Ayeka demands to know what is going on, and Ryoko calmly informs her of the truth- she was trying to seduce Tenchi.
Furious, Ayeka decides it is time to discipline Ryoko, and quickly uses her Jurai powers to summon small logs that crackle with blue energy as they electrify Ryoko. In response, Ryoko begins firing energy blasts, and the others can only watch as the two girls begin a full-blown, explosive battle.
The two seem to be fighting at equal strength, and so Ryoko decides to tip the balance- by using the meteorite as a weapon/ As the meteorite is embedded in the floor, Ryoko first needs to pull it out, a task that threatens to overwhelm her. However, when Ayeka laughs at Ryoko for not being able to lift the meteorite, her taunting gives Ryoko renewed resolve. With a mighty effort, she pulls the meteorite out of the ground, and throws it at Ayeka.
Fortunately for Ayeka, the meteorite lands on the ground just in front of her; however, the force of the impact causes it to shatter, and out from the broken crystal, something emerges- could this be the goblin of legend?
As the cave begins to collapse, a white ball of light rises out of the shattered meteorite. When the white light begins chasing them, everyone is quick to flee, but the ball continues to follow them, even when they get out into the open. Tripping on a rock, Tenchi falls to the ground, and as the ball swoops down towards him, Ryoko and Ayeka quickly jump in front to act as shields.
Emerging from his house, a surprisingly calm Katsuhito tells the ball to stop- surely it has had enough amusement for one night. To everyone’s surprise, the ball stops and takes the shape of a young woman with reddish pink hair. When she introduces herself as Washu, the self-proclaimed top scientific genius in the universe, Ayeka and Mihoshi realise they have heard of her- as a universally renowned mad scientist who was exiled seven hundred years ago. When the meteorite she was confined in then fell to Earth, the people sensed the dangerous being inside, and built the Masaki shrine as a place where it could be left undisturbed.
Washu is quick to ask who gave her such a rude awakening, and everyone is quick to point to the guilty party- Ryoko. Hearing this, Washu decides to punish Ryoko, by turning her into a cute kappa- and when Ayeka protests that such an act seems a little silly, she gets turned into a kappa too. Tenchi is quick to ask Washu to change them back, but she only seems interested in listening to him if he calls her “Little Washu”.
By the next day, Ryoko and Ayeka have been turned back to normal, but now the Masaki’s have one more girl living with them. Washu is quick to make herself at home, even turning the store cupboard into an extra-dimensional laboratory where she can catch up on her research. As Washu gets to work, Ayeka, Ryoko and Tenchi are quick to shut the door. Maybe a deadly and dangerous goblin would have been preferable to this capricious mad scientist.