When Yagami strays into the Sargasso spaceship graveyard, a mysterious young girl named Mirei secretly comes aboard and takes Sasami back to her ship so that they can play together. Believing Sasami to be in need of rescue, Tenchi and the others come after her, but soon find themselves lost in the spooky corridors of what appears to be a ghost ship! Facing their fears, the gang continue the search for Sasami, not realizing that she may not actually want to be brought back…
As the long night hours slowly tick by, Kiyone wearily flies Yagami through space- until suddenly, for no apparent reason, the ship stalls. With the engines having just been fixed, Kiyone soon realizes this is no ordinary breakdown. In their attempt to take a shortcut, they have strayed into the Sargasso ship graveyard- a place from which it is said no one ever returns.
The Sargasso is certainly a strange and spooky place. Even as Yagami drifts ahead, a mysterious pale ship materializes in front of them, and before long, strange things are happening on board as well. A poltergeist-like presence moves through the ship, scaring Nobuyuki as he soaks in the bath, and brushing the minds of the others as they rest. Finally, the presence homes in on Sasami's room, where a mysterious young girl steps through the mirror.
After gently awakening Sasami, the girl introduces herself as Mirei, and explains that she comes from the white ship now drifting beside Yagami. Mirei offers to show Sasami how she moves between the ships, and when Sasami happily accepts, Mirei takes her hand. They float up and through the mirror, with a scared Ryo-Ohki following close behind.
Unbeknownst to Sasami and Mirei, a restless Tenchi heard them, but by the time he comes in to see what is going on, Mirei is already pulling Sasami through the mirror. To Tenchi, Mirei appears as a featureless, shining figure, and Tenchi is more than a little worried to see such a creature apparently abducting Sasami. Moving downstairs, he quickly awakens Ryoko and Ayeka to fill them on what has happened.
Meanwhile, Mirei brings Sasami and Ryo-Ohki emerge through a mirror on Mirei's ship, and find themselves in a warm and welcoming room. With a wave of her hand, Mirei materializes a spread of treats and cake for her guest to eat. As they sit down to sample the food, Mirei asks why Sasami isn't afraid of her, given her strange abilities and insubstantial form. For Sasami, however, this is nothing unusual- she is used to see Ryoko phase through walls all the time.
Mirei admits that she doesn't even know where her strange powers come from. She has been alone on her ship for many years, and the only clue she has about her past is an old photograph of her that sits on the mantelpiece. Sasami is quick to admire the dress Mirei was wearing in the photograph, and Mirei happily uses her powers to let Sasami try it on for a little while.
Promising to give Sasami a tour of the rest of ship, Mirei pulls her through the mirror once more, and the room they leave behind fades into a colorless ruin. Meanwhile, back on Yagami, Washu is busy analyzing Mirei's ship. According to her readouts, its power output is zero- it is a dead ship.
Dead ship or not, Sasami is still absent, and so Tenchi and the girls head over to search for her. The group splits into three pairs for the search- Kiyone with Mihoshi, Tenchi with Washu, and Ryoko with Ayeka. The dark and deserted corridors give the appearance of a ghost ship, but whilst Mihoshi is terrified of what could be lurking in the dark, Washu is excited- she would love to get some research samples of an ethereal life form.
Moving to another mirror, Mirei and Sasami spot Ryoko and Ayeka walking through the darkened corridor. When Ayeka complains about the dark, Mirei activates the lights, allowing the Juraian princess to see both the mirror and Sasami. Not wanting Ayeka to catch up with her just yet, Sasami ducks out of sight, and the two girls run away. Puzzled, Ayeka and Ryoko examine the mirror, but find nothing out of the ordinary.
Exhilarated from dodging Ayeka, Sasami decides it would be fun to play a few practical jokes on her friends, and convinces Mirei to go along with her. Donning sheets, the two girls emerge from a mirror in front of Kiyone and Mihoshi, terrifying the two Galaxy Police officers. Sasami and Mirei throw off their sheets to reveal that it was just a joke, but the two GP officers don't notice. Kiyone is frozen stiff with fear, whilst Mihoshi has fainted!
Next, Sasami and Mirei decide to play a trick on Tenchi and Washu, by creating a ball of ectoplasm that zips around the corridor in front of them. Tenchi is suitably scared, but Washu is excited to see an ethereal life form- not to mention disappointed that Tenchi didn't grab a sample for her!
Playing jokes on the others is fun, but Mirei has an idea for something even better. After asking Sasami to close her eyes, Mirei looks into her memories and recreates the garden Sasami used to enjoy so much on Jurai. Sasami is delighted to see the garden, and the two girls happily visit all of her favorite places, including a hedge maze, fountain, roller coaster, and Earth-carousel.
Mirei and Sasami are having great fun, but even as they watch a fireworks display, Sasami realizes that she needs to go back to the others. As her mind returns to the concerns of the present, the landscape of Sasami's memories fades away, and the two girls find themselves back on Mirei's ship.
Sasami apologizes for bringing an end to their fun, but Mirei is happy that they were able to have what time they could together. Mirei thanks Sasami for the warm feeling she gave her, and surrounds her new friend with sparkles- a parting gift that will come in handy later. Saying their goodbyes, the two girls promise that some day, they will meet again.
Too tired to continue their fruitless search, Tenchi and the others have returned to Yagami. But even as they agonize over Sasami's continued absence, Mirei sends the young princess back through the mirror. To everyone's surprise, Sasami shows up none the worse for wear, despite a refusal to disclose where she was or what she was doing.
Using her parting gift from Mirei, Sasami reactivates Yagami's engines, and to everyone's relief, they are soon on their way once more. And, as Sasami looks back and says one final goodbye, it seems that Mirei is still thinking of her as well. For, where the photograph on her ship once displayed Mirei sitting alone, now it shows her together with Sasami and Ryo-Ohki. Mirei may have forgotten her distant past, but at least now she has some pleasant memories to cherish forever…