The Juraian spaceship Ryu-Oh has just received a message that the demon Ryoko is alive on Earth, and the log-like guardians Azaka and Kamidake decide it is time to awaken the ship’s captain, First Princess Ayeka. Ryoko is the very criminal Ayeka’s half-brother and fiancé Yosho left to pursue some seven hundred years ago, and as well as hoping to finally locate him, Ayeka decides that this is the perfect opportunity to apprehend this galactically wanted criminal.
Even as she makes her plans, however, Azaka and Kamidake have some news- thanks to the statute of limitations on Ryoko’s crimes, her records will be erased and her wanted status revoked in only a few seconds. Annoyed that there could be any limitation shorter than eternity, and realising that Ryoko is their only lead to Yosho, Ayeka decides to capture her anyway- they can think of a good justification later.
Back on Earth, Tenchi is still having trouble with a flirtatious Ryoko, who is looking to regain possession of the three gems on Tenchi’s sword. She explains that she needs their power to control Ryo-Ohki, the other demon from the legend, but Tenchi isn’t too happy with the idea of another demon on the loose, and refuses her request. Determined to get the gems, Ryoko tries to take the sword from Tenchi, but when she discovers that touching it causes her pain, she is forced to resort to pleading. She explains that an evil demon is coming (i.e. Ayeka), and that without control of Ryo-Ohki, they will all be in danger.
Tenchi still isn’t convinced- surely they can resolve things with Ayeka peacefully. Ayeka too initially wants a reasonably peaceful resolution, and her guardians are ordered not to fire as her spaceship appears above Tenchi’s house. However, when Ryoko ignores her demands to surrender, Ayeka loses patience and decides to start firing anyway.
With his house in danger of being blown up around him, Tenchi finally agrees to Ryoko’s request to release the gems- however, instead of giving her all three, he only hands over one, which moves from the sword to her left wrist. Ryoko isn’t ecstatic about being short-changed, but as one gem is sufficient to summon Ryo-Ohki, she doesn’t complain too much, instead using her restored powers to call to this other demon.
In response to her call, Ryo-Ohki rises out of the lake- a four pronged crystalline spaceship with an odd propensity for yowling and meowing like a cat. As Ayeka tries to destroy it, Ryo-Ohki heads for Tenchi’s house, where it teleports Ryoko, Tenchi, and even Tenchi’s house (appropriately miniaturised) on board.
Ryoko’s plan is to run away, but Ayeka isn’t about to make things easy. After an exchange of fire, Ayeka has her ship surround Ryo-Ohki with two circles of small logs. These logs seal and paralyse both Ryoko and Ryo-Ohki, allowing Azaka and Kamidake to teleport on board and capture both Ryoko and her unwilling accomplice Tenchi.
On board Ryu-Oh, Ayeka decides to interrogate Ryoko, who she has suspended upside down between the two guardians. Ayeka wants to know why Tenchi was in possession of Yosho’s sword (also called Tenchi), and when Ryoko doesn’t answer, she has the two guardians electrify her- only to discover that Ryoko is getting more pleasure than pain from the experience.
Switching off the electricity, Ayeka continues her interrogation, but Ryoko teases and mocks her at every turn. In anger, Ayeka jabs the sword into Ryoko, inflicting a level of pain that even Ryoko cannot enjoy. Finally willing to talk, Ryoko suggests that Ayeka would find out more about Yosho if she asked Tenchi about it. Unfortunately for Ayeka, there is no time- on the preset orders of her mother, it is time for her to go to bed, and to her embarrassment, she has no choice but to obey.
Elsewhere on the ship, Tenchi is having problems of his own. He is stuck in some kind of wood, and whenever he tries to leave, the trees move to trap him. Desperate to escape, he tries to hack his way using a Stanley knife, but fortunately this potentially lengthy task is interrupted by help from another source- Ayeka’s little sister Sasami. After freeing Tenchi from the trees using a controller of similar design to Tenchi’s sword, Sasami agrees to Tenchi’s request to be returned home- but only if he does a favour for her first.
After getting ready for bed, Ayeka sits down and replays the last message that Yosho sent her before he left to pursue Ryoko. They were to have been married on his return, and remembering this makes Ayeka mourn the loss of her brother and fiancé once more. With tears in her eyes, she goes to bed, Yosho’s sword clutched in her hand.
Outside, Sasami tells Tenchi what she wants him to do- he must sneak into Ayeka’s room and steal her head ornament. With no choice but to agree, Tenchi makes his way to Ayeka’s room. The princess is now fast asleep, but to Tenchi’s dismay, the ornament is still firmly on her head. Not only that, but she is also holding his sword.
Desperate to get it back, Tenchi tries to prise the sword out of Ayeka’s hand, but her grip is too firm, and after a little tugging, she wakes up. As Ayeka screams and kicks him away, Tenchi quickly runs away, with Azaka and Kamidake sent in hot pursuit after him.
Grabbing Sasami, Tenchi makes a run for it, and on Sasami’s direction, jumps into a hollow tree. The tree teleports them to another part of the ship- the same place where Ryoko is imprisoned in another tree cage. Without all three of her gems, Ryoko cannot escape, and so she requests Tenchi’s aid. Tenchi tries to explain that he cannot do anything, but as it turns out, he can. Working in the same way as Sasami’s controller, Tenchi’s sword opens the cage, releasing Ryoko.
After Ryoko and Sasami introduce themselves to each other, Ryoko decides it is time to liberate the other two gems from Tenchi, using the power of the first gem he gave her. Before she can get very far, however, the trio are interrupted- Ayeka, Azaka and Kamidake have tracked them down. After scolding Sasami for releasing him, Ayeka turns her attention upon Tenchi. She asks him about Yosho, but when Tenchi replies that Yosho was an ancestor of his who died a long time ago, she refuses to believe it.
Thinking that they are trying to trick her, Ayeka sends Azaka and Kamidake after Ryoko and Tenchi, and Ryoko responds by taking Sasami hostage. To free her sister, Ayeka has vines from the ship restrain Ryoko, and the two guardians continue their advance. As Sasami rushes over to protect Tenchi from the guardians, he raises his arms as if to ward them off; to Ayeka’s surprise, the sword in his hand glows blue, and the vines restrain Azaka and Kamidake, whilst releasing Ryoko. Ayeka realises that Tenchi is in synch with the sword (aka the master key), which could only be possible if he was a part of the Juraian royal family. Is there a grain of truth to his and Ryoko’s story after all?
Ryoko has no intention of remaining on Ryu-Oh any longer, and has Tenchi call Ryo-Ohki, who obligingly comes to get them by smashing its way into Ayeka’s ship. Tenchi and Ryoko board Ryo-Ohki, where Ryoko decides to crash the two joined ships onto Earth. That way, Ayeka and Sasami will be stranded, and she won’t have to worry about their spaceship coming after her.
Despite Tenchi and Ayeka’s protests, Ryoko follows through on her plan, and the two ships crash spectacularly to Earth, plunging into a lake and destroying Japan’s Seto bridge on the way. The story makes the news, but Tenchi is less concerned about that than about his home life. Not only was their house dropped outside the Masaki shrine, but now, they have three new house guests. Ryoko, Sasami, and even the reluctant Ayeka (who makes a futile attempt to save her ship even as it sinks into the lake) will be staying with the Masaki family for the foreseeable future. What is next for poor Tenchi?