Oh well, what can I say...? Crossover of Naruto and Monster Girl Encyclopedia. But be warned, I won't make harems and there will be male versions of many species. To the prologue!

What happens when you catch the eye of a goddess? One that got annoyed at your LOLHAX status and dickheadedness? NOTHING GOOD. Kami had been browsing through the many universes she held. Sometimes zooming in certain planets, only to spot a certain moment in a specific world. "Oho... time to make a little test~"

Kaguya tasted the boredom of the deity on her flesh and soul. Just when her sons were about to seal her away Kami had frozen time and grabbed the woman. She then tore off every last wisp of chakra and whatever else granted her powers. The Ōtsutsuki soul got shoved within the bowels of the Shinigami after she finished. The deity forever changed Ninja History on a whim.

Hagoromo and Hamura had no idea that they wasted efforts in the sealing. Both got hit with an illusion that made them see what they expected from the sealing. After recovering their energies the brothers went in separate ways. Neither knowing of what the future reserved for them.

Kami was trying to figure what to do with the massive amount of chakra on her hands. She went through several candidates in her mind until she came to a decision. "Well, just let me take this world..." It was a different version of a certain planet populated by monsters. There were handsome males along with the sexy female creatures. "Yep, a Ryū is right for what I want." Kami took a lonely egg and pushed the chakra inside. She took care to stabilize the clashing energies within and hoped it wouldn't bite her square on the ass.

She set it in the first world after she finished. Right when she was going to put each planet in their respective places... "Ah-a-tchooey!" ... "Uh oh..." She mashed them together in an irreversible way. "Hwaa... What should I do?" Time to wing it, lest her fun got spoiled beyond repair.

The Elemental Nations and its surrounding lands were all placed on one side of the planet. While on the other side was the Monster nation. It composed of two continents surrounded by archipelagoes. Two oceans separated the worlds both on the western and eastern sides.

Hagoromo had used his powers to create the nine Bijū. But the tradeoff was that his lifespan got cut to a fraction. Taking some animals he had seen in his lifetime, he gave shape to the future targets of greed for power. Each beast embodied events considered dangerous by humans, such as typhoons and earthquakes.

Hagoromo had sensed a large reading of lifeforce beyond the sea, a fact that piqued his curiosity. He left a return seal on an island, having asked his sons Isobu and Gyūki to carry him to the new land. The trip was long and tiresome, but father and child held on, rewarded by the sight of people with fish tails for legs. "Oh heavens, what is this?" Hagoromo was skeptical, while the two beasts wished to know this new location better.

The new continent housed creatures that would be seen as monsters, but they were as intelligent as humans and had their own sense of morals. They had a variant of chakra that was tinted red, much like the tailed Bijū, and a higher affinity to nature chakra. Hagoromo wondered how this fact could affect regular humans.

Hagoromo set up a return seal at a tall rock formation, linking it to the seal he left behind, creating a gateway between the two worlds. Then he made several more gateways across both continents for convenience. The Ōtsutsuki introduced them to his side, hoping for the best outcome.

The Ōtsutsuki brothers had seen the new races overwhelm the human population. Several races converted humans into new monsters for their ranks. Hagoromo feared that humans could get wiped out from the world if he didn't take the due measures. To make things worse, the Bijū had taken a deep liking to them, picking mates from races they felt attracted to.

Hamura had been much more accepting of these foreigners. He had even married a Yuki-onna after his human wife died in childbirth. He also trained many creatures that sought for his guidance. Still, some of his children and descendants were in the purely human side. They were against the integration along with his older brother.

Hamura had tried to dissuade his brother from taking such an extreme measure. "They are as human as we are, their appearance is the only difference!" But his words were for naught. "We sealed our mother for the sake of mankind, so I must do the same with these creatures." The younger twin shook his head. "And what of your children? All they have partners from these people. Can't we find another way to stop the decline?" He got pinned on the spot by Hagoromo's icy look. "There's no other way, my children must get over them, whether they like it or not."

The Bijū were tasked with wrangling the monsters to their side of the world, not knowing the goal of their father. Hagoromo used the last of his lifeforce to create a barrier that would separate monsters and humans for good. The gateway seal began failing as the twins watched each other through it. "Goodbye... brother." Hamura was disappointed at his older sibling, turning around and leaving behind his "humanity".

Hagoromo saw the Bijū pounding at the barrier, with a sullen expression on his face. They all called for the names of their spouses in distress, not knowing if they could hear. "I'm right here! Please, answer!" Their claws broke, their skin split and their bones cracked with the force they exerted, smearing blood on the invisible barrier. Their howls of anguish made their creator regret his hasty decision.

The burning hatred in Kurama's eyes made Hagoromo flinch, as the fox had never directed it to his person. "Tenko..." The leader of the kitsune, the one who taught Kurama more about himself. "He was more like a father to me than you! Even uncle Hamura knew better about how to treat family!" His golden eyes changed to a scarlet hue. "My wife... I won't see her because of you..."

Kurama faced the man and his lips rose in a snarl. "I'm not a Ōtsutsuki anymore! From now onwards my name is Inari Kurama!" He and his siblings turned around, abandoning their creator, not caring as he fell to his knees and faced his incoming death. They all decided to take the surname of their monster clans, not wanting to acknowledge their relation to Hagoromo even in name, taking separate ways and avoiding humans to grieve in peace.

Long ass fast forward past all that shit until right before the Naruto series starts.

P.s.: There will be some changes. ;)