When the king worm tells emily about The story of a child named keather, who live in the live action world and she send into the cartoon world by the unknown person.
The movie is the story of emily, a low-class 12 year old high school. At the outset of the story, a baby child named Keather is born on Planet earth, and prepared to be sent to Earth in order to destroy all life on the planet. Meanwhile, emily and her friends are on an assignment to exterminate all the life forms of Planet Kanassa. After the planet is seemingly devoid of all other life, emily and crew rest up and celebrate their victory... Until one remaining warrior catches him off guard and decides to give him the "gift" of seeing the future. This gives him the ability to see the destruction of High schoold, and almost the entire Human race along with it, at the hands of their master, demon king. Also, he sees the salvation of the planet Earth through the child keather.
Meanwhile, emily wake up in the grave of worm, when she meet king worm, a former evil villain who destroy finn's dreamcatcher, Emily wishes that the story had existed and is promptly transported into the reality created by his wish.
The episode starts with Finn waking up to Princess Bubblegum calling him her king and husband. Noticeably, the "ears" on Finn's hat are longer than usual. Finn realizes he is on the Candy Throne wearing a crown and is being watched by a group of Banana Guards, who chant, "Long live the king!" His crown floats to the ceiling, and when he looks at the group of Banana Guards again, they are upside-down except for their faces. He looks at Princess Bubblegum's shoulder and sees the King Worm. Finn thinks he recognizes the worm, who jumped out a window. Princess Bubblegum's face appears on the back of her head, and she whispers to Peppermint Butler, "He doesn't know he's dreaming." Finn is confused, and the scene changes.
Finn is sitting in a forest with Flame Princess, who calls him "honey" and tells him to eat his soup. He does not respond, so Flame Princess angrily yells for him to "eat it now!" He eats some of it and closes his eyes, and the room morphs to a room like one in the Tree Fort. Flame Princess's eyes turn into mouths for a brief moment, and she soon changes into Peppermint Butler. Holding the King Worm, Peppermint Butler then grows a second head and explains that Finn is trapped in a dream. His face then becomes blurry and his hand turns into worm-like creature who explains to Finn that he needs to find the worm and break it. Finn points out that Peppermint Butler is holding the worm, but it turns into a spoon. Phil pops up behind Peppermint Butler from his small pants, and Peppermint Butler throws the spoon at Finn.
Finn notices Jake in another room through a window, but the room appears to be upside down. Jake is wrapping a gift with Lady Rainicorn, who has two mouths and is speaking English in a very deep voice. One of her mouths spits out tape that Jake uses for the gift. Lady Rainicorn then tells Jake to play his viola, and he does. A music note comes out, then turns into the worm. Finn sees the worm escaping through a small hole in the wall and jumps in the room after it. He and Jake start to talk, and they realize that they are in a linked dream with one another. Jake states that he does not think Lady Rainicorn is real, and they decide to follow the worm through the hole, which is a problem because the hole is too small.
Jake explains that because it is a dream, Finn can do whatever he wants. He then imagines a sword capable of blasting a hole in the wall and is happy with himself for not dreaming up weird stuff. The sword then turns into a shark and Finn freaks out. Jake tells him that he needs to be careful, because if he fills the world with his subconscious fears, it will fall apart. Jake tells him to just shrink down, and the two of them go through the worm's hole.
They wind up in a field with Ice King running towards them. Ice King calls them Fionna and Cake and tells them that he has really made a mistake. Finn and Jake are confused until two monsters made up of a bunch of penguins show up. Finn and Jake run away until they find their dad, Joshua, who is not responding to anything they say. Joshua starts knitting, and eventually his knitting turns into the King Worm. King Worm then bolts to a nearby mountain, and Finn imagines that he and Jake have gigantic legs. Jake complains that it is boring for him as it is his normal power, so Finn imagines that he has a bird instead of legs. As they chase after King Worm, it starts raining Lumpy Space Princesses. When they reach the top, they find a frozen King Worm. They grab a nearby rock that appeared from nowhere, break the worm, and the dream fades away.
Finn and Jake "wake up" in their room and start asking one another if they're okay, and they celebrate that they did it. (Notably, the "ears" on Finn's hat are still longer than usual.) Finn then notices a mirror wavering in the background, and upon closer inspection realizes his reflection is Farmworld Finn. He says that he's pretty sure that it was not normal. Jake then tells him that it is fine, but when he turns, his nose is huge. Finn then points at a full mug that's falling to the floor, breaking, and then reversing back to its initial state repeatedly. Finn realizes that Jake pinched him earlier, but he never pinched Jake back. He starts trying to pinch him, but Jake backs off, telling him that everything is fine. When Finn finally catches and pinches Jake, his skin melts off, and Finn realizes for sure that he is still dreaming.
King Worm then rises from the melted Jake and says that Finn cannot defeat him. He proclaims that he will keep Finn in the dream-scape until he has consumed all of his "life energy." Finn yells that he uses that and starts to attack, but he realizes something is missing and gets depressed. He sadly states that he will be stuck in the dream-scape forever, revealing a significant fear. The ceiling cracks and a chunk falls on King Worm's head. He tells Finn to "knock it off" which causes Finn to remember what Jake said about fears breaking down dream-scapes.
Finn concentrates on his deepest fears, and saltwater begins to pour from his navel and fill up the room. The Lich then crawls out of his bellybutton, and Finn freaks out. The clearly deteriorating worm tells him to calm down, to which he replies, "Never!" Princess Bubblegum comes out of his stomach next. Finn starts to feel relieved until she tells him to quiet down because she is having coffee with The Lich and that he would not understand because he is "too young." This freaks him out even more and causes more damage to the worm. He then goes into a crib and remembers Ghost Lady (Shoko) and continues to be horrified as the worm deteriorates to near nothing. He asks the King Worm to stop one final time, but the worm claims he does not know what Finn is talking about. Finn strains and a clown pops out of his navel. The dream breaks as the worm is shriveling up even moreso, and Finn is with Jake in his living room with the shriveled King Worm and his minions; the minions suddenly explode. Finn then orders the worm to get out of his house in a manly voice, and the worm meekly complies. Finn pinches Jake to be sure he is awake. Jake crosses his arms and walks away, saying, "Come on!" Finn replies that he just did so to check, and Finn's dreamcatcher was broken into pieces by king worm, king worm had his done as the story end, emily was shocked, that the dreamcatcher was destroy, so king worm give emily a rainbow heart gems so he can turned darlyn into rainbow heart warrior.
Emily bring her friends to give darlyn a elements, but until she and friends sees a people are dead
Killing many of his minor soldiers and sending the Final Spirit Cannon to demon king himself, emily seems about to change the future. However, demon king counters this with his Supernova, which kills king worm (who save emily and friends), many of his own soldiers, and destroys Rainbow heart city itself, all while uttering a maniacal laugh. As he is dying, king worn sees one more vision of the future: keather facing demon king. Being assured that keather would be the one to kill demon king; king worm gives a small smile as he disintegrates along with the planet. As the planet is on the verge of blowing up, demon king continues laughing at its destruction, as well as telling Dodoria and Zarbon to watch the "beautiful fireworks" (in the English version, he reacts as though he were watching a spectacular performance from a play, though this is corrected in future dubs of this scene). After his demise, King worm wishes emily,friends and keather, to take care. At the same moment, emily and friends, who is still in the space pod, wakes up.
Elsewhere, having just completed an assignment on a far-off world, bella is informed by tom (in the English version it is one of demon king's minor soldiers who tells him) of his homeworld's destruction. His pride keeps him from expressing his shock, and he remains outwardly emotionless and she watch Kai and friends are freezes in time. Soon afterward, keather's space pod touches down on Earth, where she is found by her real parents, and giggles happily in the man's arms. Mr. De guzman then decides to care for the two as their own daughter, and renames her darlyn. The film ends with a montage of darlyn's many heroic deeds on Earth, leading to his battle with demon king.