Since 2004, BIONICLE has been a clear example that there really isn't a clear line between science-fiction and fantasy. Up through 2003, BIONICLE was fairly obviously pure fantasy. There was no attempt to explain Kanohi or elemental powers as science; they were simply magical powers. Then came Metru Nui. While more science fantasy than science fiction (airships, Kanoka, etc. were not intended to work using Earth physics), it was the first real attempt to 'explain' the powers and abilities the characters had. The only thing remotely close before this was the energized protodermis used to transform the Toa Mata into the Nuva. Then, in 2004, everything was protodermis of one type or another, so everything could be explained away. Even in '06-'08, when the setting was much more fantasy (or perhaps post-apocalyptic sci-fi), a quasi-scientific explanation was attached to everything. In '09 and on, it was almost entirely fantasy... yet it was still labeled science fiction. And herein lies the problem. Claiming things work because of an unexplained substance with completely unknown and, at times, blatantly fantasy-like (ex. energized protodermis acting differently on things depending on their destiny) properties is no better than simply claiming things work because of magic. No attempt has been made to explain protodermis, and no such attempt shall ever be made. There are systems of magic more rigid in their rules than protodermis! To pull an example out of the air, how about Brandon Sanderson's Final Empire series? [spoilers ahead for those who haven't read the Final Empire books] There are three distinct classes of magic: Allomancy, Feruchemy, and Hemalurgy. If you're an Allomancer, you can swallow metals and 'burn' them to give certain powers (somewhat like Kanohi, but they run out eventually and you have to find new metals). If you're a Feruchemist, you store physical or mental attributes in metals to use later. And Hemalurgy can give regular people Allomantic or Feruchemical powers. But could any BIONICLE fan give you a list of exactly what purified or energized protodermis can do? Do we know anything about how they work other than a list of powers consisting of hundreds of radically different powers? Is there any logic, any scientific basis at all for BIONICLE physics? Or is it just a jumbled collection of fantasy powers labeled as sci-fi to look cool?

[Note: this is not intended to malign either BIONICLE or fantasy in general. I have nothing against fantasy; I simply disliked BIONICLE labeling itself as science fiction.]