The protagonist awakens in a stark, white, marble-like room with no memory of how he arrived or even who he is, despite wearing a school uniform. He possesses extensive knowledge but no personal memories, leading him to speculate about a life filled with typical school archetypes. A disembodied voice, possessing great authority, reveals that the protagonist was not brought into the room but rather "born" there moments ago. This voice, which identifies itself as a god, explains that this is a different world called Im Navar, similar to Earth but with its own unique lifeforms and a drastically different evolutionary path.
The god has summoned the protagonist to fulfill a request. He is informed that he has been reborn as one of the thirteen Demon Lords who currently rule Im Navar, a world embroiled in constant conflict between the Demon Lords and other races. The god's request is not for conquest or destruction, but for the protagonist to construct a massive, impregnable dungeon in the "Demon Lord's Blood Tears," a desolate wasteland situated between the Human Continent and the Demon Continent. This dungeon would serve as a buffer zone, potentially halting the perpetual warfare. The god explains that the world suffers from an extremely short average lifespan of 32 years due to constant war, poverty, and underdeveloped medical technology, despite the existence of magic. The god's ultimate motivation is to alleviate the burden of guiding souls to the afterlife.
Initially overwhelmed and hesitant, the protagonist, who identifies himself as a weak, ordinary human, tries to refuse. However, the god emphasizes that as a Demon Lord, he is inherently an enemy to the world and that the proposed dungeon location would be his safest refuge. To aid him, the god bestows upon him a smartphone containing a "Dungeon Creator" app and grants him immense power. The protagonist receives "Magic Spring," "Divine Protection," and an array of powerful magic and crafting skills, including "All Top-Tier Attribute Magic," "Spirit Magic," "Time-Space Magic," and max-level blacksmithing and alchemy. He is also given the name Amdusias.
The protagonist begins to construct his dungeon, starting with a spacious living area and a path leading to the surface. He discovers that the dungeon interior is environmentally controlled and that the smartphone system, "Dungeon Creator," can communicate with him. He learns that the dungeon is connected to the sea and that he needs to extend it to secure a water supply. The system warns him about the presence of creatures within the dungeon's area.
Upon extending the dungeon to the coast, the protagonist accidentally incorporates several monsters, including goblins, orcs, redcaps, and an ogre, into his dungeon. He decides to summon the ogre, hoping to recruit it as his first companion. The ogre, a solitary traveler with a single horn, reveals a history of discrimination and hardship due to its perceived weakness. The protagonist, emphasizing his rejection of prejudice and his desire for companionship, successfully recruits the ogre, named Amdusias, who becomes his first ally and the beginning of his journey as a Demon Lord. The ogre's narrative highlights the harsh realities of its life, marked by neglect and ostracism, making the protagonist's acceptance a profound turning point for it.
