On the Dark Side of the Moon, Hanazuki hears a noise emanating from the Mouth Portal. She turns back to find out what it is, only to discover that a pink, sloth-like Alterling had just appeared. Hanazuki, surprised by its cuteness, decides to hug it. After a while, the Alterling still holds on to Hanazuki, and it drags her through the Mouth Portal.
She and the Alterling find themselves on an unknown moon, and the Alterling lets her go. There she sees another lime green Alterling, holding a boombox. Hanazuki asks them what are they trying to tell her, but the music is too loud, so the pink Alterling turns the boombox off. The Alterlings get in a fight, and Hanazuki tries to calm them down. Suddenly, a Moonflower descends from a diamond. Hanazuki greets her, and asks her if the Alterlings also brought her to this moon. The Moonflower corrects her, saying that it is actually her moon. She tells Hanazuki her name is Miyumi, and introduces her to her Slooths. She also introduces her to Beebs, or BB for short, a slooth who hands around her and snaps.
Remembering that the Slooths brought her for a reason, Hanazuki asks Miyumi if everything is okay on her moon, to which Lime Slooth plays dramatic music on his boombox. Miyumi answers that everything is "fabulous", claiming her moon to be the best in all the Lunaverse. She tells Hanazuki to enjoy herself, to which the young Moonflower agrees. Miyumi is already eagerly planning a big party, but Hanazuki suddenly notices her Moodgleam glowing Lime Green. Hanazuki isn't sure if everything is okay like Miyumi makes it out to be, as she has a bad feeling, but Miyumi insists that everything is fine. Hanazuki follows her as Miyumi climbs to her diamond. Miyumi tells Lime Slooth to turn the music on, and he does.
Hanazuki and Miyumi take a trip around the diamond-filled moon, with Hanazuki being speechless about how great Miyumi's moon is. Miyumi agrees. Hanazuki suddenly sees a strange chrome symbol on the ground. Miyumi also sees it but has no idea what it is, and dismisses it as unimportant. Pink and Lime Slooth show up, with the boombox playing dramatic music. Pink Slooth holds on to Hanazuki, worried. Miyumi, oblivious to all this, asks Hanazuki what does she want to do next, and Hanazuki answers they should do anything she says.
Hanazuki and Miyumi visit a field full of lollipops, and Hanazuki can't decide on what lollipop to taste. Miyumi accidentally sticks a lollipop on Lime's eye when she tossed it aside after licking it once, and Pink takes it off. Hanazuki's bracelet glows lime again, and Miyumi asks her what that color is. Hanazuki, now really worried, asks Miyumi if she has never been scared of anything, not even the Big Bad, but Miyumi never heard of him. Hanazuki explains it to her, and tells her she will help Miyumi grow Treasure Trees to protect her. Miyumi tells her that she does have Treasure Trees, and Hanazuki finds them, only to discover that they're powerless because they have been neglected. They are also all teal, as she only feels glamorous. Miyumi boasts, saying that she'd like to see the Big Bad take her moon down. An upset Hanazuki tells Miyumi her trees are sick, but Miyumi understands "sick" as in "awesome". Hanazuki tells her that they are sick as in they don't have power, and won't help her fight the Big Bad. Hanazuki tells Miyumi that the Trees must be gooped in order to be cured.
Hanazuki, Miyumi and the Slooths gather all the Goop they can find. Hanazuki asks Miyumi if she has more Slooths, to which she says yes, but she hasn't seen them in a while. Back at the Treasure Tree place, they goop the trees and they recover. Suddenly, they notice BB isn't there. At the river, Miyumi sees BB's necklace and a chrome symbol, and Hanazuki notices a spaceship flying by. Miyumi glows blue with sadness because she just realized that her Slooths are gone. Hanazuki comforts her, telling her that "feeling it" is the first step to rescuing them.
Suddenly, Little Dreamer comes flying down and gives a Treasure to the two Moonflowers. Miyumi accidentally drops her Treasure, and a Blue Treasure Tree appears. Miyumi cries, thinking her life is not fab anymore. Hanazuki offers her to come to her moon, but Miyumi rejects the offer since her Slooths were taken away from her, and she didn't notice. She assumes responsibility, so she will stay and protect her moon. Miyumi gives Hanazuki the boombox, telling her to "pop some tunes" if she ever needs them.
Hanazuki thanks the Slooths for bringing her to the moon, feeling sorry for their missing friends, and tells Miyumi she's not the only one who has missing Alterlings. She thought the Big Bad took them, but now they have a clue. Hopeful, Hanazuki glows raspberry and tells Miyumi to have hope. Miyumi, glowing blue, hugs her. Hanazuki tells Miyumi that blue and teal are a great combination, to which she agrees.
On a post-credits scene, the Hemkas are dancing to the music of Miyumi's boombox, but Sleepy Unicorn can't sleep, so he uses his magic to turn it to a slower tune. Red Hemka turns it back once he falls asleep and continues dancing.
- Miyumi grows her first Blue Treasure Tree.
- In the Surprise, Surprise's episode, is a reference to the mysterious noise heard in the Mouth Portals and in the episode of Oh My! Miyumi! It was discovered, the noise actually came from a Boombox that held a Lime Green Slooth on a distant moon and is Miyumi's moon.