From the introduction:
Welcome to the world of Pokémon! This world is inhabited by incredible creatures with amazing abilities called Pokémon! For some people, Pokémon are pets, others use them to fight, while a few study Pokémon as a profession.
...Of course, this particular world is far more sexual then ones that you might be more familiar with. Pokémon and humans are far more physically affectionate both with their partners and each other, battles have a tendency of devolving into hardcore fucking, and professors and their assistants run all sorts of lewd experiments on Pokémon and even people to fulfill their desire for perverted knowledge. Your very own Pokémon legend is about to unfold! A world of wet dreams and lewd adventures with Pokémon awaits! Let’s go!