SPOILERS AHEAD of the 4, 5 and 6 episodes After the sixth episode, I finally figured it out. Here is my theory: the red energy is a fragment of Raava. I suspect that, following the cataclysm, Raava was shattered by the power of the storm—which explains why there was no reincarnation cycle for 250 years. The writers have already debunked the theory that child Avatars were being hunted, and it has also been confirmed that the theory about the Avatars traveling to the future is incorrect. Therefore, the Avatar cycle could not resume until a sufficient portion of Raava had been recovered to restore it. I am convinced that Vaatu would not grant visions of the past to Nisha or Pavi. The only logical conclusion is that this is a fragmented piece of Raava—specifically, her root chakra. Since this chakra is blocked by fear, it radiates fear to those nearby; yet, it does not seem to intend to harm the Avatars—perhaps it seeks to reunite with them? Further evidence lies in the fact that this fragment has four vertices—corresponding to the four petals of the root chakra—and is, notably, red. This was a clever ruse to mislead the audience into believing it was Vaatu, when in reality, it is simply Raava’s blocked chakra. Furthermore, the final chapter of the first book is titled "Root Chakra"; it feels as though everything is connected. Ultimately, I believe we will encounter other parts of Raava’s chakras, each corresponding to the specific color and number of petals associated with that chakra. Instead of appearing as petals, they manifest as triangles—this fragmente was forming a square (since four triangles make a square)—which suggests they have become corrupted. The Avatars' mission will be to restore each of Raava’s chakras; I suspect that Korra herself fragmented them to protect each of the sanctuaries—which is why, in the opening sequence, they appear in their respective colors. As for what caused the cataclysm, I don’t know yet—but my guess is that either spiritual energy was misused, much like Kuvira did, or the third spirit portal somehow disrupted the planet’s energy flow.