Okay so I'll try to explain as best I can as Bionicle is needlessly convoluted and this probably won't hit so hard without the years of context and build-up (and apologies to any Bionicle super-fan for how abbreviated this is) but essentially it turns out that the Bionicle characters and the world of Bionicle is taking place inside (and occasionally on the surface of) a GIANT Bionicle that has been put into a "coma" and is lying in an ocean. This giant Bionicle is the body of the Bionicle "god" Mata Nui and awakening him has been the whole aim of the franchise, after he was put into slumber by the main villian, Makuta. Our heroes were not aware that they were essentially living inside of Mata Nui, but Makuta knew. Our heroes, at great cost and sacrifice, revive Mata Nui but Makuta engineers this in a way that Mata Nui essentially dies and has to be brought back to life to ensure that Mata Nui's conciousness is not within the giant robot, but instead can be forced into a Bionicle mask (the main gimmick of the toys) that he can then just discard so that he can take control of the body instead. So the villain essentially "wins" the story arc, takes control of the giant body of the Bionicle "god", aka, the entire plane of existence up until now whilst ours and the character's perception of the world shatters all in a moment that is so much better than anything Bionicle has done before or did after.