The story begins in Ice Land, where a nameless deliveryman flees a horde of NightmareDemons while carrying a parcel. The man fears he is running out of time, exclaiming the parcel is meant for the Devil Child who will gather the "seven horns" and save the world.
Meanwhile in the Real World, the date is July 31, 2000, 2:06 PM. Setsuna Kai loses a kendo match against Mirai Kaname, sparking a heated argument between the two. Their friend Zett Takajō tells them to stop fighting, and reminds Setsuna that his mother Tsubomi is watching over him. Zett refers to Setsuna's pendant, which his mother gave to him as a child before she passed away. Since then, Setsuna has vowed to become strong.
As the three walk home, snow falls upon the city, which has been happening across the world since the day before. Setsuna wonders if it is the work of ghosts, but unbeknownst to the kids, the Nightmares from Ice Land secretly observe them. Setsuna retreats to his apartment to warm up, when suddenly, the deliveryman crashes through the wall, hands over the parcel, and dies. Nightmare then enters the apartment, addressing Setsuna as the Devil Child possessing a Messiah's Horn. Grabbing a broken piece of wood, Setsuna strikes Nightmare's neck, only to have it turned against him and stabbed through his heart. Nightmare takes the Messiah's Horn, the true name of Tsubomi's pendant, causing Setsuna to erupt with rage. As a pentagram flares on his forehead and his wounds get miraculously healed, he quickly reaches for the parcel. The packaging erupts into flames and transforms into a Deviliser, which Setsuna fires at Nightmare, blasting him out of the apartment.
In firing the Deviliser, Cool the Cerberus appears before his new master. He tells Setsuna that the unnatural weather is due to Demons from Makai, the Demon realm, and how Makai and the Real World are both in peril. To save both worlds, a Devil Child must gather the seven Messiah's Horns. Setsuna is reluctant to fulfill such momentous duties, being a mere elementary schooler, until Nightmare returns to kill him. Cool gets injured by Nightmare's Zan spell, calling for his master to be brave and hone his powers. Motivated by wanting to become stronger, Setsuna open a rift to Makai using his Messiah's Horn, while Cool fights back by casting Agi. With Nightmare defeated, Setsuna and Cool leap into the Makai rift. Mirai overhears the conflict and smirks, knowing that things are now in motion. As for Zett, he sees explosions coming from his friends' apartment complex, and enthusiastically says "Game Start."
Chapter 2: Excessive Expectations
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Setsuna has a faint flashback to his childhood, wherein he was beaten up by bullies and vowed to kill them. He has a brief memory of young Mirai, until Cool distracts him and welcomes him to Makai. The rift brought them to Ice Land, which Cool claims is Makai's sixth stratum. Standing before the Ice Gate, or the "Door to Hell" as Cool puts it, Setsuna learns that by using a Vinecom, he can load Demons into his Deviliser's Memory Bullets and summon them. The two march into the Ice Gate, declaring they will save both Makai and the Real World. In the distance, another Nightmare and his Demon gang discuss how their master, Hel, said there are three humans in Makai. Suddenly, their attention gets directed to Mirai, who has entered the Demons' realm with a Deviliser.
Setsuna and Cool arrive in Frost Town, to which Setsuna exclaims how Makai is a lot less grim than he had assumed. Taking a lunch break, Cool further explain his master's importance, in that only people with power like Setsuna's can use the Messiah's Horns power. There are seven horns in total, which must be combined with the seven Messiah's Eyes to form the Norn Keys, items capable of bending everything to the wielder's will. However, the remaining horns are scattered, and Cool fears that the world is doomed if the Great Demon Lord acquires them.
Chapter 3: White and Blood
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Chapter 4: Straight to Hell!!!
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Chapter 5: Those who Shed Tears
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Chapter 6: A Calm and Quiet Place
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Chapter 7: Wandering People
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Chapter 8: Outbreak of War
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Chapter 9: Path to Destruction
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Special Manga: ChilTalk
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Chapter 11: Dark Forest
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Chapter 12: Dearly Beloved
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Chapter 13: Ominous Warning
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Chapter 14: Future in Motion
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Chapter 15: Domination
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Chapter 16: To the World and Friends
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Chapter 17: Those Worthy of Living?
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Chapter 18: True Colors
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Chapter 19: Relentless Anger
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Special Manga: ChilTalk Red Book Rip-off
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Chapter 21: A World on the Bound of Darkness
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Chapter 22: Final Point
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Chapter 23: And Now, to the Ultimate Fight...
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Chapter 24: The Dark Opernball
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Chapter 25: Journey of Light and Darkness
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Chapter 26: Final Evolution Zwei
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Chapter 27: Only One Truth
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Chapter 28: The End and the Beginning
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Chapter 29: Peace Be With You
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Special Manga: ChilTalk if....
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