Dressed as a Pokémon and Summoned by Serena

My name is Song Jie, and I have traveled to an elven world with a city as the background. But why did he become an elf? Fortunately, I awakened the infinite evolution system and was able to evolve into the mythical Nine Tails! And he also turned Serena into his own shit-sweeper! … My name is Serena. After the end of the world war between elves, I was reborn and traveled to a parallel world. But fortunately, this parallel world is similar to my original world. And I discovered that as long as my elf becomes the strongest, I will have a chance to go back and save my world. But when I chose the elf, I obviously chose the round land shark, why did it become Eevee? Also, what's going on with this guy's growing tail? It's different from what I remember! This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.