"Fate/Grand Order -mortalis:stella-" is a manga adaptation of the popular mobile game "Fate/Grand Order," focusing on the game's prologue and early chapters. The story is set in a world where humanity's survival is threatened by the incineration of human history. The protagonist, Ritsuka Fujimaru, is a rookie Master recruited by Chaldea, an organization dedicated to preserving humanity's future. Alongside Mash Kyrielight, a Demi-Servant and Ritsuka's loyal companion, they embark on a mission to correct anomalies in history known as Singularities.

The narrative begins with Chaldea's discovery of the impending destruction of humanity in 2016. Through the use of the Near-Future Observation Lens, Chaldea predicts the incineration of human history and identifies Singularities as the cause. Ritsuka and Mash are sent to the first Singularity, Fuyuki, a distorted version of a Japanese city engulfed in flames. There, they encounter hostile Servants, heroic spirits summoned to fight for Masters, and uncover the machinations of Lev Lainur, a traitor within Chaldea who orchestrated the Singularity's creation.

As the story progresses, Ritsuka and Mash travel to other Singularities, including the Roman Empire during Nero's reign and the French countryside during the Hundred Years' War. Each Singularity presents unique challenges, with historical figures reimagined as Servants, both allies and enemies. The duo forms alliances with legendary heroes like Jeanne d'Arc, Nero Claudius, and Cu Chulainn, while confronting powerful adversaries such as Gilles de Rais and the enigmatic King of Mages, Solomon.

The manga delves into the dynamics between Ritsuka and Mash, highlighting Mash's growth as a Demi-Servant and her struggle to understand her purpose. Ritsuka's role as a Master is also explored, emphasizing their determination to protect humanity despite their inexperience. The narrative balances action, historical intrigue, and character development, staying faithful to the source material while expanding on key moments and relationships.

"Fate/Grand Order -mortalis:stella-" serves as an accessible entry point for newcomers to the "Fate" franchise while offering deeper insights for fans of the game. It captures the essence of the original story, blending high-stakes battles, emotional character arcs, and the overarching theme of humanity's resilience in the face of extinction.