"Attack on Titan: Lost Girls" is a spin-off manga series set in the world of Hajime Isayama's "Attack on Titan," focusing on two key female characters, Annie Leonhart and Mikasa Ackerman. The narrative is divided into two distinct story arcs, each exploring the personal struggles and backstories of these characters.

The first arc, "Wall Sina, Goodbye," centers on Annie Leonhart. The story takes place during her time as a Military Police Brigade member stationed in Stohess District. Annie is tasked with locating a missing noblewoman named Carly Stratmann, who has mysteriously disappeared. As Annie investigates, she uncovers Carly's hidden life and the societal pressures that led to her decision to flee. The arc delves into Annie's internal conflict, her sense of isolation, and her complex relationship with her father, providing deeper insight into her motivations and the emotional burdens she carries. The investigation also subtly ties into the broader themes of the "Attack on Titan" universe, such as the rigid class structures and the moral ambiguities of duty.

The second arc, "Lost in the Cruel World," shifts focus to Mikasa Ackerman. This story presents an alternate reality where Mikasa never joined the Survey Corps and instead lives a peaceful life with Eren and his parents in Shiganshina District. However, this idyllic existence is shattered when Titans breach the walls, forcing Mikasa to confront the fragility of her world and the inevitability of loss. The arc explores Mikasa's deep attachment to Eren and her struggle to reconcile her desire for a normal life with the harsh realities of their world. It highlights her resilience and the emotional toll of her protective instincts, offering a nuanced perspective on her character.

Both arcs are grounded in the psychological and emotional dimensions of their protagonists, providing a more intimate look at their inner lives while maintaining connections to the larger narrative of "Attack on Titan." The series enriches the main storyline by expanding on the personal histories and motivations of Annie and Mikasa, offering fans a deeper understanding of their roles and struggles within the broader conflict. The tone remains consistent with the original series, blending moments of introspection with the ever-present tension of a world under siege.