4. Recreational Sex
Now we get to the crux of the matter, and one that isn't exactly easy to address in-world.
"Why is it fine for humans and pokemon to have sex, and why does it happen so damned much?"
I have read more than a couple of stories where pokephilia is either recently outlawed or recently legalised. The only real issue I have with this concept is 'why'? Why has this only occurred now, rather than 10 years ago, or 100 years ago? What has changed that has prompted this? This is one of the things that has motivated this companion piece, because the answers to those questions are not necessarily easy to put into a fap-fic without changing the tone quite a bit.
The first, and simplest, explantion is "Because that's the kind of fic I wanted to write".
But my personal justification for it goes a bit deeper than that, and I do apologise if I start to lose people here, but I'll start by addressing the most common arguments against.
First, and most common: "But pokemon are like animals!" and the logical lead on from that "How can animals give consent?" I will start by saying I do not in any way advocate any kind of non-consensual sex. In real life, this argument is correct, animals do not have the capacity to give consent, and so don't have sex with animals.
Hopefully you will notice, however, that I have tried to highlight at least some of the major reasons why pokemon can safely be treated as not-animals. A pokemon in partnership with a trainer will, ideally, have at the very least near-human-level intelligence. They are quite obviously able to understand human communication quite clearly, and in turn are able to communicate themselves. This gives them the ability to quite clearly demonstrate whether or not they consent to a sexual encounter and in many cases, the ability to initiate one themselves.
In most cases, given the difference in levels of self-defence, one would instead assume that it would actually be the human at risk, as most pokemon have numerous ways of violently expressing their discontent, if need be.
The second argument is a little more general, and amounts to "Ew, sex is bad/a sin/embarrassing etc." In this case, the shunning of recreational sex is a societal construct, in many cases stemming from the tribal need for population control and the prevention of sexually transmitted infections.
My personal justification for the ridiculously sexually active societies I portray is that people in the pokemon world never really developed that aversion to sex. One of the hallmarks of intelligent life is the ability to make the distinction between sex for pleasure and sex for procreation – and as I have tried to make clear, pokemon can be considered well above the threshold for this.
Taking into account the in-game breeding mechanic and the existence of 'egg groups', we can see that a large fraction of pokemon can have inter-species recreational sex without fear of producing offspring. This does not eliminate the issue of STIs, but in all honesty no sickness of any kind is really encountered in the games – so for the sake of simplicity I'll follow that example.
As for the frequency of this recreational sex, it really comes to down to availability and time. At the lower ends of civilisation, most of a being's time can be assumed to be spent trying to survive, with relatively small amounts of free time. In addition to this, the pool for potential mates (barring incest) is similarly small. But as we progress down the figurative technological tree, more and more time is freed up, and more and more other beings are encountered that are potential mates.
Fast forward to the equivalent of modern times, and we have the large fraction of people and pokemon free to pursue whatever interests them. And alongside this, we have a society where sex is treated as something that is significantly less taboo. We can jump to a (reasonably) logical point at which sex is treated by many people as something between a sport, a hobby and an expression of affection. It's not the sort of thing you do with literally every person you meet, but if you like the cast of someone's jib, so to speak, they're fair game.
This is not to degrade the ideal of a committed sexual relationship – in my opinion, it actually strengthens it. The idea that your partner/s are all you need, that they satisfy you without need for outsiders, that you identify with them outside of the sexual side of the relationship – those facts will still be just as important.
And the partnership between the trainer and their pokemon should inherently foster this kind of relationship. The level of trust involved, and the shared experience – and, in all honesty, the rush that comes with winning – would all foster a closer relationship between partners.
Once you get past the issues inherent in the possibility of sex, the only obstacle is the writing. My personal favourite clichés are "Oh no, my pokemon went into Heat, whatever should I do?" or "Wow, you're really excited after that gym battle, I should give you a hand!" or even "Wow, you looked really hot beating that irritating guy into the ground for me, come let me ravish you." But my job here is to try not to write a story that's not just another clone of every fap-fic out there. Or, if I'm going to do that, then to do it well enough that you read it anyway.