Rini asks a shocked Sailor Moon, Venus, and Tuxedo Mask to help her save the Earth of the thirtieth century. The little girl explains she is from Crystal Tokyo and has traveled through time, looking for help to save her mother. Luna speculates that the Black Moon and captured scouts might be in the future as well. The cats urge Rini to tell more, and Venus asks to be taken to the thirtieth century. Rini hesitates and acts scared, so they go home to rest.

Rini goes home with Darien, and Bunny follows. He puts Rini to bed, and then talks with Bunny. Suddenly, she points out that Rini loves him, but cuts off, saying she shouldn't be so jealous, especially when her friends are missing. Darien comes up behind her and hugs her. They whisper how they want to protect each other and kiss.

Luna and Artemis sleep over at Mina's. Luna dreams as she sleeps of a time when she found a door in the Silver Millenium, and Queen Serenity explained it led to a forbidden land, and must be forgotten.

When Rini wakes up, she asks Bunny and Darien to go with her to the future. They gather in the park with Venus, and Rini takes out a key, which she explains is the Key to the Fourth Dimension. She tells the others of the danger and to hold her hand, no matter what. Rini calls out, and a flood of light carries them off. Sailor Moon slips away from Rini.

Sapphire gasps as he realizes the Rabbit has traveled through time with some companions. Prince Diamond calls Wiseman, who instructs them to destroy the Silver Imperium Crystal and the castle. Emerald volunteers to do so, but Rubeus chuckles at her and calls on Chiral and Achiral, the Artificial Jewel Brothers. They come and plan to use Code 005: Operation Remake.

Sailor Moon, Tuxedo Mask, Venus and Luna wander about the space of time travel, lost without Rini and her key. However, the Crystal in Sailor Moon's brooch glows, leading them to a door. They are stopped by a mysterious scout, Sailor Pluto, who tells them they must die for time travel, which is forbidden. Right before Pluto is going to execute them, Rini comes running up, crying out not to kill them. Pluto calls her "Small Lady."

Rini apolgizes to Pluto for stealing one of her keys and explains why they are all there. Sailor Pluto apologizes to the group, and leads them through the door, staying behind herself, the solitary gaurdian of the last taboo.

The group enters Crystal Tokyo of the thirtieth century, finding it quiet and desolate. The buildings have been melted and the people lay on the ground, seemingly dead. Rini explains there was an explosion and then all the buildings crumbled, and everyone but herself collapsed. She then leads the way to the Crystal Palace.

They all enter the glittering palace only to find it empty. They are greated by the Artificial Jewel Brothers who tell them this is only a mirror image of the palace. Achiral splits into multiple forms. Sailor Moon gets mad, and does her "Moon Princess Halation!!" but it does nothing. Suddenly they are all frozen, held at a molecular level. Emerald comes in to taunt them into giving her the Crystal. Tuxedo Mask hears a voice that tells him how to break the crystal at their feet holding them. The Jewel Brothers cry out as their palace comes tumbling down. Venus unleases "Venus Chain Encircle" as Tuxedo Mask attacks with "Tuxedo the Smoking Bomber!" Emerald gets away, but the Jewel Brothers are killed.

The group is lead by Rini into the real Crystal Palace. Inside, they see a crystal encasing someone who looks to be an older Princess Serenity. Rini tells them she is Neo-Queen Serenity. Then, a small grey kitten comes up to Rini, who she calls Diana. Entering from the side is a figure who looks like Tuxedo Mask, but wears a more elaborate jacket. Sailor Moon and Tuxedo Mask look on in shock.