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 is a demonic asteroid from outer space that is full of demons inside. Every 500 years, the Grim Comet would travel close to. 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. First in 1005 AD, the two beast kings joined forces and came up to the palace of Sesshōmaru's mother's until later that evening since the Grim Comet fragment entered the Earth's atmosphere and approaches to the palace, they destroyed it by Kirinmaru's Blasting Barrage and Tōga's Meidō Zangetsuha. 500 years later in the Sengoku jidai, 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 came to same place in the right spot in the right time, they destroyed the large fragment of the comet with Sesshōmaru's Bakusaiga's destructive ability and Inuyasha's Meidō Zangetsuha.

14 years later in the feudal era, Kirinmaru spotted the Grim Comet as 500 years later in the. Noticed by Kirinmaru's second daiyōkai incarnation Osamu Kirin, he takes notice that humans such as Sōta Higurashi cannot perceive the comet in the modern era. Even though he felt that he had a connection with Kirinmaru between two eras in which that he stated that the Grim Comet "does appear in the other era as well".

After the demons went extinct in the modern era, Osamu saw the comet is getting closer to Tokyo, in which from Kirinmaru, the Grim Comet would inevitably collide with Earth, indicating that the humans will become demon fodder and become nonexistent, ending in apocalypse of the degenerate age which the Tree of Ages intends to have the Half-Demon Princesses and their parents prevent at any cost.

After Grandpa Higurashi checks the Sacred Tree as he sees the seals blew that something is wrong inside the trunk because of Sesshōmaru and his haku, he looked up in the sky as he saw the Grim Comet is coming, even for Osamu. After Osamu killed three Shibugarasu, he sees the Grim Comet is approaching to the atmosphere.

Trivia

 * On the 500th year, they see a glowing red star at night which means that the comet approaches to Earth in Episode 15.
 * The comet approaches every 500 years than the ordinary s approaches every 470 years according to Osamu Kirin.
 * 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.
 * In Episodes 39, 40, and 41, the Grim Comet's tail's color goes to rainbow than red in episodes 15, 22, and 23.