As she walks the streets of Tomobiki-Cho, Shinobu Miyake sadly ponders how it seems nothing ever changes.
Walking by some trash cans, she finds a handsome young man requesting food. When she rummages in a grocery bag for something, the young man grabs for a raw carrot and consumes it. Shinobu also sees that the young man is dressed in a large bunny suit. She quickly attempts to leave, but the young man wants to repay her. Wanting to get rid of him, she sends him skyward, where Lum sees the young man disappear through a subspace portal. As she flies down to meet Shinobu, the two find a strange key the young man left behind.
Meanwhile, the young man, named Inaba, has returned to a group of rabbits at the Destiny Production Management Bureau. It is then that the others find Inaba has lost the key. At first they are upset, but then realize that no normal humans could ever be able to use it.
Unknown to them, Lum has found a way to rig a door to utilize the key, and she, Ataru, and Shinobu end up plummeting into a world of multiple doors.
The door they enter into shows a future where Sakura and her boyfriend Tsubame are married with children. However, the futures for everyone else is rather shocking when Shinobu sees she's married to Ataru, and Lum to her old boyfriend, Rei! Ataru is also incensed when he finds he's employed by Shutaro Mendo! As the 3 see their possible futures, Inaba shows up, but all vehemently refuse to accept such a future. Inaba claims that there are other futures through other doorways.
In order to move through subspace, he leads the others to a locker room, to change into appropriate subspace attire. Ataru receives a rabbit suit like Inaba's, while Lum and Shinobu's outfits are more reminiscent of a Playboy bunnygirl's.
The next future they go to shows a world in which Ataru is employed by Shutaro, with Lum having married him. Shinobu meanwhile, appears to have no romantic prospects. The group them plunges through other doorways, but find nothing good. Lum laments that there isn't a single future in which she and Ataru are married.
It is then that Inaba reveals that there is a way to create 'futures.' Taking them to a room, the 3 use rods to turn glass into doorknobs that will create an ideal future. Each of the group makes their own doorknob, but before they can use them, the subspace rabbits capture them. Lum, Ataru and Shinobu are caged, with Inaba to be boiled alive as punishment for letting them in and creating the doorknobs.
Shinobu however, uses her strenth to free to others, and make off with Inaba. The chase leads them through subspace, where Lum loses her doorknob. Ataru uses his, and finds a world where his dream of a harem has come true...albeit in a cramped apartment. However, in his future, Lum has left him, and he quickly exits the dream and throws away the knob...before Lum finds him and attempts to zap him.
Shinobu has used her doorknob to hide both her and Inaba from the other rabbits. However, Inaba is rather surprised to find that her future is very 'normal,' as if her normal life had never changed.
Meanwhile, the other rabbits have caught up with Lum and Ataru. Using a giant key, they set all the subspace doors to fall and lose their powers. One actually opens and Ataru and lum fall in...only to find a future in which they are married! Ataru attempts to save the door, but to no avail.
The group manages to escape, and finds a door leading back to their time. Inaba sends them through, but closes the door behind them. Shinobu sobs as the door closes, worried at what may happen to Inaba.
Sometime after, Inaba appears to Shinobu, explaining that his punishment has been reduced to repairing the subspace door room. The two then go off to have tea.
The short ends with Inaba putting door knobs on new doors. As he does, he finds Lum's doorknob, and places it on one of the possible 'future' doors, before continuing his work.