Grim Comet

"To warn you a great cataclysm is approaching. Every 500 years, an object known as the Grim Comet travels close to this earth. Unfortunately, large fragments start to break off and descend from its core."

- Riku

The Grim Comet is a demonic asteroid from outer space that is full of demons inside. Every 500 years, the Grim Comet would travel close to Earth. War and famine would spread the land, causing the deaths of many people. Since the human population was declining at the time, the yōkai population was on the rise and this made two powerful Daiyōkai control them in the East and West. One being Tōga, ruler of the West, and the other, Kirinmaru, ruler of the East. The two beast kings joined forces and destroyed a fragment of the comet by Kirinmaru's Blasting Barrage and Tōga's Meidō Zangetsuha.



500 years later, the Grim Comet traveled close to earth once again, and because Tōga is no more, and Kirinmaru has fallen into a long slumber, the sons of the Great Dog Demon joined forces and destroyed the large fragment of the comet with Sesshōmaru's Bakusaiga and Inuyasha's Meidō Zangetsuha.

500 years by the Reiwa Era, the Grim Comet appears again. Noticed by Osamu Kirin. Osamu takes notice that humans such as Sōta Higurashi cannot perceive the comet in the modern era.

Trivia

 * It seems the comet can't be detected by Modern technology, as there was no broadcast announcing a "new" comet being spotted in the sky.
 * As no powerful demons exist in the Modern era, and with the portal in the Bone-Eater's Well shut, there's no way to get Towa, Setsuna, Sesshōmaru or Inuyasha there to help even if he was freed from the Black Pearl.