Author's note: this was a weekly prompt of "Where do babies come from?" This assumes pokemon can understand each other and have some semblance of language among themselves. I do not own pokemon, nor any characters within this story save Kanade.
"Where do baby pokemon come from?" Trainer Kanade's Tropius Mucai asked Kanade's Munna, Baku. He looked at her confused. Baku was wise despite having hatched the same time as he did. He sometimes wondered if it had to do with her unusual coloration. Perhaps instead, it was because she was a Psychic type. Mucai wasn't sure why, but she knew more than he did.
"Why do you wish to know?" Baku looked at him confused, then followed his gaze. They were walking through a town and passing a human woman carrying a young child. "Ah, I see... we come from eggs." Her answer was soft, as she cared deeply for her friend and didn't wish to offend his feelings, but curt. She didn't see need for more explanation than that.
"Well, yes. I remember seeing the shells after we hatched. I watched others hatch in the day care not long after. But where did those eggs come from?" He stopped walking, causing Kanade herself to hesitate. The trainer knew the two of her pokemon were close and carried on conversations she couldn't comprehend. She just smiled and waited, assuming it was something important.
Baku frowned, though it was hard for the casual observer to tell due to her drooping snout. "I was told this story once, but I am not sure if it is entirely true. You may wish to sit as it will take a bit to retell it all."
She took a deep breath, mentally preparing herself. Mucai sat on his haunches and cocked his head curious as to this great tale she had heard and the origins of it. "Once, when we were at a pokemon center, two towns back, when Nurse Joy had taken you in the back for a checkup I asked a Chansey that was taking a break why they are often carrying eggs. I asked if they lay the eggs of every kind of Pokemon."
"The Chansey laughed and said she was just watching the egg a while for a couple." At Mucai's confused look, "lovers, two pokemon, one boy, one girl who care deeply about each other." He nodded, seeming to have another question but deciding to keep it to himself for now. Baku continued her story, "Chansey told me that when a couple of pokemon care for each other very much and wish to raise a baby alongside their trainer, they sneak off into the night. Under the moon the dance together and roll up a ball of mud."
"Mud?!" Mucai's look of complete disbelief was caught even by Kanade. Whatever her two pokemon were discussing it must have been pretty interesting. The Munna laughed, a high pitched noise similar to a squeal.
"I didn't believe it myself either at first. Anyways she said they put something special to each of them in the ball of mud, sometimes their own fur or scales, sometimes a gift from a trainer or a ribbon they earned, a favorite berry. Then they wish really hard and both use their strongest special attacks at the same time on the mud-ball."
By now he was looking at her like she was telling a grand joke. Kanade snickered in the background, watching them talk despite not understanding a word of it. "Believe it if you will, I'm telling you what I heard. Anyways, if their wish is granted, Celebi comes and turns the mud into an egg. It then contains a baby, that is similar to either parent. After a while it hatches."
He mulled it over a bit, "so that's how babies are made?"
She grinned and nodded, "that's how babies are made!"