Disclaimer: I don't own Pokemon, it is owned by Nintendo. I don't own Undertale, it is owned by Toby Fox.
Book 1: SeaBlue
Prologue
A 10 year old boy wakes up groggily. Wondering what happened, he sits up and sees a yellow mouse standing upright, right in front of him. To the boy's surprise, the yellow mouse begins to speak.
"In the world which you are about to enter, you will embark on a grand adventure with you as the hero.",said the yellow, nameless mouse,"Speak to people and check things wherever you go, be it towns, roads, or caves. Gather information and hints from every source. New paths will open to you by helping people in need, overcoming challenges, and solving mysteries. At times, you will be challenged by others and attacked by wild creatures. Be brave and keep pushing on. Through your adventure, we hope that you will interact with all sorts of people and achieve personal growth. That is our biggest objective."
"Let your adventure begin!",said the yellow mouse before vanishing, with what appeared to be some old guy wearing a lab coat appearing in its place.
"Hello, there! Glad to meet you!",said the old guy,"Welcome to the world of pokemon!"
"My name is Oak.",said Oak, who was for some reason, named after a tree,"People affectionately refer to me as the Pokemon Professor."
...A professor named after a tree... Just what has the world come to?
"This world...",muttered Oak,"...is inhabited far and wide by creatures called Pokemon!"
"For some people, Pokemon are pets. Others use them for battling.",said Oak,"As for myself... I study Pokemon as a profession."
"But first, tell me a little about yourself.",said Oak,"Let's begin with your name. What is it?"
"Red.",said Red, softly
"Right... So your name is Red.",said Oak, suddenly, a different 10 year old appeared right next to Oak,"This is my grandson. He's been your rival since you both were babies, which I still can't figure out how that's possible. ...Erm, what was his name now?"
"Blue.",said Red, softly
"...Er, was it Blue?",asked Oak,"That's right! I remember now! His name is Blue!"
Suddenly, Blue vanished, and was replaced by a 10 year old girl.
"This is your friend. You've been friends since she moved here.",said Oak,"Um, what was her name again?"
"Leaf.",said Red, softly
"Leaf it is then!",replied Oak,"Red! Your very own Pokemon legend is about to unfold! A world of dreams and adventures with Pokemon awaits! Let's go!"