It all happened when Altina who is stationed at Bordertown Tuonvell which is north of the Belgaria Empire. She was planning to be an empress but she needs a strategist to advise her.
This is where Momonga meets Altina and their journey begins to help Altina wish to become an empress.
At Bordertown Tuonvell, north of the Belgaria Empire, Altina, commander of the border regiment and the princess is eager to welcome a certain "person." Riding a wagon disguised as a commoner she meets the Overlord of Death, Ainz. Confused she believes this is the man she is supposed to meet. Ainz tells her not to worry and knows that she is looking for a strategist and is here to fill that requirement. She inquires if he was transferred from the imperial capital only to be told that he was exiled from another world.
The two travel through Tuonvell, Ainz tells her about his world, though she finds the idea of buildings as tall as the sky to be doubtful. It begins snowing and their horse has sprained its leg. Ainz pulls out a potion from his cloak. During that time she briefly notices his skeleton hand until she is distracted when Ainz uses the potion to heal the horse's leg, surprising her on its recovery. Ainz explains it to be magic, which Altina believes only exists in stories.
Suddenly five wolves appear Altina takes a fighting stance while Ainz comments on the hounds' cuteness. Altina warns him that they are savage animals, Ainz taking note of their hostility uses [Dragon Lightning] to kill their leader. The wolves leaders fall causing the pack to scatter.
His casualness in slaying the beasts shocks Altina who becomes angry. She scolds Ainz for killing the wolves with such power, stating that the beasts are needed to dissuade bandits from the area. She makes him promise her not to use offensive spells freely. Nevertheless, she thanks Ainz for saving her and the two continue on their journey. Altina wishes to know more about magic, though Ainz tells her only magic casters can cast magic and judge by her face she is more suited as a warrior. Altina takes the statement too literally and believes that the face is the denominator. In addition since magic doesn't exist in this world, he doubts Altina could use it. Altina believes that he the strategist she is looking for. She tells him that she wishes to become empress to liberate the citizens from tyrannical rule.
The two arrive at Fort Sierk where Altina's superior General Jerome is station. Ainz knows it would be a simple matter to kill the incompetent man, but doing so would make it difficult for others to acknowledge Altina as the commander. So Ainz uses his magic to cast spells to enhance Altina's abilities. Though hesitant to uses such advantages Ainz convinces her to do so in order to use his full abilities as her strategist. Altina wins the fight against Jerome with one hit. Jerome and the rest of the men acknowledge her as the leader, just as an attack from the barbarians reaches the walls of the fort.
The barbarians lay siege on Fort Sierk. Seeing their predicament Altina allows Ainz to use his magic on the condition he does not kill the barbarians. Ainz casts [Garvity Bound] on the attackers, causing an earthquake that scares off some of the barbarians. Altina decides to attack the opposing Fort Volks and employs Ainz's assistance to accomplish the task. Fort Volks being known as an invulnerable fortress casts physical negation magic on Altina and opens a [Gate].
Ainz and Altina enter through the [Gate] alone and infiltrate the fortress. They encounter Zechmeister who attacks AInz but due to his undead body is unharmed. The young knight is then immobilized by Ainz and the two meet the command staff of the fort who attempt to mount an attack on the invaders but are easily defeated.
After the conquest of the fort, the two turn to the Imperial Capital of Belgaria and conquer it. Altina becomes the new Empress. Her reputation was spread amongst the populace, be it the nobles, commoners, and even foreign nations, as a feared new empress who gained the power of a demon king.
Regis, Altina's strategist apparently is rudely awakened by Altina. The previous events were all part of a dream Regis was having. The dream was based on a new book he had been reading: Overlord.
- This is the first official crossover story between Overlord and another work.