The television anime series A Wild Last Boss Appeared! is set in the year 2800 within the world of Exgate, a realm that was once the setting for an online game. The story begins when a man wakes up to find himself inhabiting the body of Lufas Maphaahl, also known as the Black-Winged Tyrant, the Great Conqueror, and the leader of the Twelve Heavenly Stars. Lufas was a powerful character and player-created "last boss" who was supposedly defeated two hundred years earlier in a large-scale player event by a group of seven heroes. However, the man soon realizes that Exgate is no longer just a game; it has become a real, living world where the inhabitants have their own wills and histories, and the consequences of actions are permanent. The world is now on the brink of extinction due to the rise of a powerful Devil King, and Lufas's previous reign of fear has left a complicated legacy. The protagonist, now stuck in the body of this infamous overlord, must journey across Exgate to find answers about why he was summoned and to locate her former loyal vassals, the Twelve Heavenly Stars, who have disbanded in the years since her defeat.

The main character is Lufas Maphaahl, a beautiful and overwhelmingly powerful being with distinctive golden-red hair and jet-black wings, which mark her as an aberration among her winged race. Her personality is a duality; she is remembered in history as a merciless tyrant who conquered the world, but in truth, she is generous and indulgent towards her allies, though she remains brutally ruthless to her enemies. Inside her mind is the consciousness of an ordinary man from Earth who once played her as a character in the game, and his more relaxed, modern perspective blends with her innate overbearing and regal mannerisms. Accompanying Lufas is Dina, a self-proclaimed advisor and former decor artist who has been guarding Lufas's empty base, the Sky Tower Mapal, for two hundred years. Dina is somewhat klutzy and often forgettable to others, but she is knowledgeable about the current state of the world and possesses useful transfer magic.

The central narrative arc follows Lufas as she seeks to reunite her scattered and long-disbanded subordinates, the Twelve Heavenly Stars. The first major companion to be found is Aries, a timid, sheep-like boy who was once a weak creature but has grown into a formidable and loyal warrior over the centuries. Another key subordinate is Libra, a golem maid who serves as the base's guardian. The story explores the power dynamics of this new reality, where humanity has lost its war against the demon tribes and the seven heroes who defeated Lufas are now either dead, cursed to be at half-power, or otherwise incapacitated. The world's overall power level has drastically declined, leaving Lufas, who is currently operating at a capped level of 1000, as an overwhelming force capable of obliterating most obstacles. As Lufas travels, she not only battles new enemies but also confronts the consequences of her past actions, including monsters and disasters that were unleashed upon the world following her supposed death.

Notable narrative arcs involve the re-recruitment of her former generals, which often requires defeating them in combat or proving her identity. One early arc focuses on locating Aries, who has been hiding for years, and another involves reaching a weapon cache that modern adventurers are too weak to access. The story also delves into the mystery of the protagonist's summoning and the true nature of Exgate. Flashbacks and discussions among characters reveal that the original defeat of Lufas was possibly a staged event, a final blaze of glory orchestrated by the player and his friends. The anime also introduces characters from the current era, such as Sei Minamijūji, a new hero summoned from Earth to oppose both the demon threat and Lufas. Unlike the overpowered beings of this world, Sei is of a low level and average ability, but his ethical thinking and refusal to blindly follow the "goddess's script" allow him to take an unconventional path, opening the way for dialogue and reconciliation rather than simple combat. The series thus blends action-heavy sequences of Lufas effortlessly dispatching enemies with world-building that explores political intrigue, the nature of heroism, and the gap between historical legend and reality.