Let’s take an example.  Squirtle can pronounce two syllables: “squirt” and “tle.”  He can vary pitch and inflection to convey questions, exclamations, commands and so forth, but in terms of constructing indicative statements he seems to be limited to those two sounds, which means that he’s basically speaking in binary.  What’s more, 90% of what he says is just alternating those two syllables – he tends to say “squirtle squirtle” over and over rather than mixing it up the way Bulbasaur or Pikachu do (which is why I’m talking about Squirtle – when I talk about Pikachu people have an annoying tendency to worm around with the different combinations of syllables he uses, and how he has a unique utterance for Ash – pikapi – as though there could possibly be some way this had escaped my attention).  We know from Island of the Giant Pokémon that those two syllables are sufficient for him to express dissatisfaction, contentment, cynicism, humour, mockery, familiarity, uncertainty and disdain… and to comment on the weather.  If those two syllables are really all he has to work with, the range of states of mind he manages to convey over the course of that story is linguistically impossible.  Clearly there is some other component to the way he’s communicating that we aren’t capable of picking up on, but damned if I know what it is (shifts in pitch and inflection too subtle for a human ear to interpret reliably?  Body language?  Pheromones?  Some combination?).  That episode’s useful as a case study for a lot of questions because of the subtitle thing, but it’s hardly the only time we see Pokémon having conversations, and you can usually at least guess what they’re talking about (see, for instance, the scene between Bulbasaur and Pikachu in Bulbasaur’s Mysterious Garden) – they’re far from being dumb animals, and they can express their concerns to each other with, apparently, a fair degree of eloquence, in spite of possessing a minuscule lexicon.

The biggest issue for me here is that I just don’t believe there’s a whole lot we know for sure about Pokémon reproductive biology.  You can see what I have to say about that in this article here – and while I would be the first to admit that a lot of what I say in that piece is a little bit ‘out there,’ I think it does demonstrate fairly well that this is a tricky topic at the best of times (since the time of writing, we’ve also been slapped with the random NPC in Coumarine City who says that Pokémon eggs aren’t eggs at all, which is such a bizarre out-of-context statement that there’s little you can do with it, but could easily be Game Freak saying “yeah, whatever you think you know about this stuff is wrong”).  What this all boils down to is that I’m not sure whether Pokémon would be capable of desiring humans in that sense, or even whether they would necessarily have the requisite… er… bits… with which to act on it (even Humanshape species).

Having said that, let’s talk about this anyway for the sake of argument.  Inter-species breeding is certainly common among Pokémon, and in the real world humans often get different animals to breed and produce hybrid offspring like mules or ligers.  This kind of thing even happens without human instigation from time to time.  And then you have that… regrettable incident with the chimpanzee and the frog (a union which is not going to produce offspring no matter how you slice it)… Anyway.  I think the main reason we get upset when humans indulge in such activities (aside from the straightforward visceral revulsion – or, to put it in everyday terms, “eww!”) is that it’s just kind of an abusive action at its base level, because the animal probably doesn’t fully understand what’s going on and in many or most cases wouldn’t be able to do anything about it if it did – which on ethical grounds puts us in a similar position to sexual relations with children (again, eww).  If the Pokémon is the instigator, which I suppose could happen, then maybe there’s a mitigating factor there, but I don’t think you can get away from the fact that a trainer/Pokémon relationship is not entirely equal; I think most people in the Pokémon world would probably agree that the trainer is in a position of power or authority here.  A lot of Pokémon respect and look up to their trainers and habitually seek their approval; that’s really not a healthy starting point.  I believe the most appropriate real-world analogy would be a teacher/student relationship – sure, sometimes the student comes onto the teacher, but that doesn’t make it okay!  The proper response is to say no, firmly, and get the student transferred to another class (i.e. trade the Pokémon, because as well as you might work together, no good can come of that $#!t).  Alternatively, since a lot of Humanshape species are Psychic-types, people might easily suspect a reversal – I think that if such a relationship were ever publicly known, allegations of untoward Hypnosis or similar psychic manipulation would fly fast and thick, possibly ending with the institutionalisation of both trainer and Pokémon.

In sum: I actually don’t believe this would be common, and honestly I’m not certain it could happen at all, but if it did there are still serious ethical issues involved and the best course for the trainer is to avoid such entanglement at all costs because, really, letting something like that happen is not good for either partner, and although it might not have quite the same stigma as bestiality in the real world, I strongly doubt it would be received well (because, again, eww).

I suppose the simple answer would be that I’d aim at least initially for a degree of professionalism – trainers always have expectations of their Pokémon, so it’s only reasonable that the Pokémon should be able to expect certain courtesies, services and assistance in return – with the caveat that any professional relationship is smoother if it’s also friendly.  I think my answer to this question has a lot that would interest you.

Now, as for what Pokémon “call” their trainers – bearing in mind that we don’t actually understand how they communicate, since they just don’t have enough phonemes for all the concepts they obviously understand, that’s tricky.  For a variety of reasons, I don’t believe Pokémon understand or have any use for the concept of personal names, so actually I think all Pokémon likely refer to their trainers as something like “human,” “master,” or “friend” (and yes, I know about the episode with the subtitles, and I know Pikachu has a specific sound for Ash – translation is a bit more complicated than that, even when going between two human languages).  You do raise an interesting point, though – different species will have different needs in this relationship and will react differently to trainers – even the anime tends to put this down to variations in individual personality, as do the fans, but differences in the psychology of entire species must be important too.  Lucario, I think, are supposed to be solitary by nature – a highly social Pokémon like Mightyena, famed for teamwork, will almost certainly need a great deal more micromanagement in training and more interaction with other Pokémon to maintain a balanced emotional state, while a Lucario might be happy being left to meditate for hours on end.  To take an extreme example, Kangaskhan, a Pokémon evolved for a very high degree of investment in her young, might come to view a (comparatively) small and frail human as a family member in need of maternal protection, and consequently be uncomfortable letting her trainer out of her sight for an extended period.  And then there are Pokémon that are just plain inscrutable, like Starmie or Sigilyph – even a very skilled trainer might have trouble figuring out what kind of relationship makes them happy.