The world of the novel.

The continent of Erno is a land where people live in both flat and mountainous areas. It's a medieval world with a strong hierarchy of status, where chivalry, swordsmanship, and of course, magic flourished. Mana was an important form of power in this world, where even a peasant with a large supply of mana could become a royal magician with effort. The class hierarchy was strict; the nobles did not accept peasants into their ranks, condemning and despising them, but remaining silent. The highest authority, in the person of the imperial family, in turn, paid no attention to the indignation among the nobles. Strength was highly valued in a world where there were regular waves of demons attacking the people. As the novel's plot unfolds, two main characters appear on the scene—the Crown Prince and the Holy Maiden, who will stand at the forefront against the demons. The Crown Prince was renowned for his strength and vast mana reserves, making him resilient in protracted battles with demons. The divine healing of the Holy Maiden, in turn, helped wounded soldiers and magicians heal their wounds and restore their mana. But despite the strength of the people, according to the novel's plot, the waves will only grow longer, and the demons will attack even more, leading to the final downfall of the people.

Waves is the name given to the demon attacks due to their sporadic yet regular assaults on the Empire. The demons' goal is to conquer human territory and subjugate the inhabitants; failing that, they destroy everything in their path. Lower-ranking demons are stupid and behave primitively, like mindless animals, but higher-ranking demons possess remarkable intelligence. The higher-ranking demons control the lower ones like puppets. At the head of the demon forces is the Demon King, somewhat similar to a human – the most dangerous and powerful demon, often operating behind the scenes. Demons use a dark substance called "magi," not mana. The difference between magi and mana is that magi is drawn from the very essence of a demon; therefore, the higher the demon's class, the greater its power. They are cruel and merciless, lacking pity and compassion even for their own kind. Demons can only be killed by striking their heart or severing their head; otherwise, they quickly regenerate from their wounds.

This world also contains dragons, elves, dwarves, and beastmen. They inhabit certain parts of the continent. They ignore the war between humans and demons, neither hindering nor aiding them.

Blake is an illegitimate child in the Blake family. His family constantly oppressed and despised him, considering him an eternal obstacle in their path, so he grew up embittered by the world. In the original plot, he is a villain who subtly pulls the strings and hinders the main characters due to his inferiority complex. But the soul from another world that entered Blake's body is a completely different person who entered the world of the novel he read after dying in an accident in his own world. Blake knows the entire plot in advance, knows how to act in different situations, and how to thwart the demons or the main characters, depending on which side he chooses.