(Pokemon anime setting) + (starts in the Sinnoh Region) + (the true starting location is Alola) + (answers Arceus's summons) + (not a dark story)
Alola Region
In an independent laboratory at Aether Paradise
“At last, this great experiment is complete! You've worked hard, Darkrai,” the white-haired young man calls to Darkrai, who is maintaining the device.
Then he glances at Marshadow, happily munching on a Dragon Fruit nearby, and says, “I'll be away for a while! Everyone, be good! And Darkrai, when Celebi gets back, make sure it eats properly.”
With that, the white-haired young man jumps into the Ultra Wormhole. But perhaps the Ultra Wormhole itself is unstable, because he doesn't enter it.
Instead, he arrives in another world, one where Pokemon exist only in movies and video games!!!
In Story Two
During class in Room Five of Year Three, a black-haired boy named Meng Yuan is playing with his newly bought Darkrai plushie when a spatial fluctuation knocks him unconscious.
When he wakes, he finds an alpaca in front of him. He kicks it and realizes it's real, only to be blasted away by a jet of spit...
A palace from the start. How am I supposed to become a Pokémon Master!!!
If it looks good, just watch it. Come on, the author is great. Just so-so, that's it