Talk:Race/@comment-680972-20180709114101/@comment-45.56.46.26-20180709163733

Heteromorph doesn't necessarily mean they can transform/shapeshift.

It means that the underlying biology is sufficiently different from a 'normal' creature that it is inherently "monstrous". A goblin is basically explicable in terms of chordate biology, a dragon isn't even before you get to the whole magically transforming business. A werewolf or slime or whatever can change shape, but the real issue is that they do it much faster than is possible for ordinary organisms. A giant spider or insect may seem plausible but actually ignores fundamental cube/square limitations (and tesserect/square issues as well, if you want to get picky about the internal organs as well).

Basically, if you could explain a race sheerly by appealing to established biological principles, it can be a demi-human. If you need to resort to magic to make it work, then it's a heteromorph. The magic can be necessary just to enable the creature to function at all (giant spider), or to carry out some simulated biological function (rapid transformation or unlife), or it can be basically an add-on (angels/demons with innate spells/magic abilities).

That's also why humaniods and demi-humans can't interbreed, but either can breed with at least some heteromorphs. Heteromorphs can't exist in the first place except by magic, so as long as their innate magic allows breeding with other races, they can do it (BTW, this is probably why Demiurge and Albedo have no qualms about her ability to get pregnant with Ainz's child, as a succubus the underlying nature of the sex act is a transfer of magical energy anyway, so whether she uses that energy to feed herself or to conceive, it's still innately magical...I'm not sure the same mechanic holds for True Vampires, but since they count as undead but can reproduce it probably must).