Over a century ago, astral mages under persecution from the Empire banded together and established the Nebulis Sovereignty under three founding families: Lou, Hydra, and Zoa. With the leadership of Millavair Lou Nebulis VIII, the Sovereignty aims to minimize casualties in their conflict with the Empire—a stance the extremist Zoas disagree with. Tensions rise between the families as the upcoming election to decide the next leader approaches. The Zoas are willing to do anything to achieve success; however, a world-ending war may ensue should they be victorious. Princess Aliceliese Alice Lou Nebulis XI has no choice but to cooperate with any potential allies in order to advance towards her ultimate goal of ending the conflict that has long tormented everyone involved. This includes Iska—one of the Empire's greatest warriors and her greatest rival.

Nikola is just a village girl working at the inn...until the day dragons invade, and she meets Haga, a scholar of everything around him. He's a part of an elite society called Seeker, created to address a series of maladies plaguing their usually peaceful world. But both Nikola and Haga have secrets they hide...ones that will change each other's very existence... (Source: Kodansha USA)

Under the belief that the omnipotent god Mitama will come to save him, Yukito Urabe participates in a ritual to become the new leader of his father's cult. But when the boy drowns during the ritual, he wishes to be reborn in a world without gods or religion. Reawakening in a completely different world devoid of spirituality. He meets a deviant girl named Aruaru, who introduces him to her village. However, his idyllic image of this world's society is short-lived when he witnesses a public group suicide and learns of the country's end-of-life system: at any moment, the government may order any citizen to die. Aruaru and her sister are forcibly taken for execution soon after, prompting Yukito to rush to their rescue—but to no avail. In a moment of desperation, Yukito recalls his father's teachings and utters a prayer for Mitama to save them. Seemingly answering his call, a little girl descends from the sky and annihilates everyone who harmed Yukito and his friends. To Yukito's surprise, the girl introduces herself as Mitama.

The world's greatest assassin had sworn lifelong allegiance to the organization that raised him. However, despite his loyalty, that very same organization takes action to silence him, ultimately leading to his demise. Drowning in frustration and regrets he can no longer suppress, he finds himself in an audience with a goddess attracted by his exceptional skills. The goddess offers him reincarnation into a magnificent world of swords and magic so he can perform a crucial mission: prevent that world's destruction by slaying its hero. Accepting the goddess' request, he is reborn as Lugh Tuatha Dé, the son of a noble family of assassins serving the Alvan Kingdom. Under the guidance of his father, Lugh learns new assassination techniques that significantly differ from the cold-blooded and unsympathetic killing style of his previous life. Furthermore, his other talents bloom, allowing him to meet new allies and acquaintances. Even so, Lugh knows that his efforts are far from adequate, because a monumental adversary such as the hero can only be defeated with perfection.