Reborn in Naruto As Madara's Grandson - Chapter 9: Failed Schemes

The elf girl, Aria is an adventurer. Her enchanting, lovely features attracts everyone. Her twin peaks are ripened to the point of exploding. Then, being embraced in between those twin peaks was a little animal… his name is Tama.

He looks like to be a cat at first glance, but Aria and her surrounding companions failed to take notice of single detail. Tama, he’s a human who’d reincarnated, given a second chance at life. His true form, it’s not that of an ordinary cat. Instead, he’s a monster of the strongest class, an extremely young behemoth.

Aoki’s resolute face was indifferent. “If the sun doesn’t shine on me, please let me be surrounded by darkness!”
From a different perspective, look at the entire Pokemons world.

- Description from Uukanshu

At the genesis of the world, the ‘Dark God Entropy’ was defeated in the fight between the five other Gods, and was sealed.