It should’ve been a normal morning for Rosalia, the subtly named Roselia; go to an opening within the forest, absorb plenty of sunlight, perform photosynthesis, and carry on with the rest of her day.
But today, there was a Swellow perched on one of the tall trees in the surrounding area, and being a sizable bird of prey, pounced on Rosalia as she was soaking in the sunlight. Rosalia reacted promptly, releasing spores that paralyzed the bird, giving her time to run away. However, Roselia aren’t known for their speed, and the attacking Swellow was able to stave off the paralysis for a turn and claw Rosalia. This caused her to reflexively release even more spores, some poison powder and sleep power, neither affecting the already paralyzed Swellow.
However, there was another spore released, one Rosalia had not seen before. Suddenly, the Swellow shrank to the size of the Roselia. The bird squawked in fright, and Rosalia knew whatever spore that was, it was her key to making it out of this encounter on top. So she released more of the powder, shrinking the Swellow smaller and smaller until it was the size of a tiny leaf. The bird tried to fly away, but Rosalia gave it a well deserved smack with her flower. When the Swellow fell to the ground, the Roselia loomed over it in her moment of triumph. As the Swellow flew away in fear, she knew that her days of being preyed on were long over.
Rosalia spent the rest of the day cheerfully running around, shrinking anything bigger than her. Some of the forest pokemon tried fighting back, but she used her relatively large plant body to knock them out, gain experience and leveling up. At some point, she learned a peculiar new move: growth. She was curious and tried it out, and while for most Pokemon it merely raised attack and special attack, for Rosalia, it also raised her height, nearly doubling it. In a moment of intrigue, she used it more and more, expanding rapidly and towering over even trees. It was no longer that Rosalia was large in comparison to the shrunken pokemon, she was large. Rosalia jumped with joy, causing the foliage surrounding her to quiver. After being a small target for so long, she could dominate the entire forest, bending it to her will.
After a while of admiring her new power, Rosalia started to shrink closer to her original size, although still much larger than usual. She laid down comfortably, knowing any pokemon that dare interrupt her slumber would be shrunk down to the size of an atom.
Meanwhile, a report was just made to a council of legendaries, informing them about a giant Roselia going on a spree of shrinking pokemon and rampaging through a forest.
Rosalia woke up to a very sunny day, ready to toy around even more with her newly-discovered powers. She frolicked across the forest, shrinking any mon that was clumsy enough to attack the seemingly weak Roselia. She then grew herself to be massive and cheerfully danced around, enjoying her size to the fullest, before laying down, using her flower hands to rest her head on whole looking at the clouds, many of which Rosalia was now bigger than.
She was then interrupted by a massive blast, too strong to be from any pokemon native to this forest. Rosalia turned around to see a very angry Dialga, readying a massive beam. She tried to evade it, but the beam was homing and the Roselia was unable to dodge it. Rosalia found herself losing a lot of her size as she felt weak, with the Dialga readying another attack. Quickly, Rosalia released all the pollen she could muster, shrinking Dialga down to the size of a pebble.
Dialga was distraught, with no way to grow back to its normal size, unlike the Roselia who now loomed in front of it. The god of time tried to run away, but Rosalia stomped on it in a moment of triumph.
Rosalia figured that if Dialga attempted to confront her, then more legendaries would surely follow. So, the Roselia knew she had to grow herself to an unstoppable size. Rosalia used growth, then used it again, again, again, and again. The ground around her started to crumble and shake as the Roselia grew massive, with her shadow and grassy body looming over the surrounding landscape. Sure enough, more legendary Pokémon arrived at the scene, but Rosalia just kept growing bigger, bigger, and BIGGER, and stepped on all the puny legendaries that tried to take her down.
Rosalia, after vanquishing these threats, continued her ascension, growing from the size of a mountain, to the size of a country, and then to the size of a continent as she laid herself on the northern hemisphere of the planet. She admired her massive size and loomed over the world, looking at all the tinies beneath her. She had grown to the size of a goddess, and Rosalia thought about being praised like a goddess. She emitted even more pores, not for shrinking or inflicting status conditions, but pores with an aroma. As the aroma spread all across the planet, any Pokémon or human that got its scent became infatuated with the Roselia. She shrank herself down to the size of a city to see, and was greeted by the sight of her new servants worshiping her.
And so, Rosalia became the massive goddess of this world. Anyone who tried to defy her would promptly be shrunken down to an incomprehensibly small size, while her loyal followers would remain devout. They constantly surrounded her and showered the Roselia with praise. They had constructed a massive throne and flowerbed, fit for the size of the goddess, and were now working on her palace, which would be bigger than the size of any metropolis. Rosalia had fun occasionally growing to the size of the planet once more, and sometimes to the size of their sun, as her eyes loomed over her worshippers, her kingdom. She chuckled, this was quite the upgrade from being bird food.