"Attack on Titan: Lost Girls" is a spin-off manga series that expands on the world of "Attack on Titan" by focusing on two key female characters, Annie Leonhart and Mikasa Ackerman. The narrative is divided into two distinct story arcs, each providing deeper insight into their personal struggles and motivations.

The first arc, "Wall Sina, Goodbye," centers on Annie Leonhart. Set before the events of the main series, it explores Annie’s life as a Military Police Brigade member stationed in Stohess District. Tasked with a mission to locate a missing noblewoman, Annie’s investigation reveals her internal conflict and the weight of her responsibilities. The story delves into her interactions with Hitch Dreyse, her partner, and the moral dilemmas she faces as a soldier and a warrior. The arc highlights Annie’s isolation and her struggle to reconcile her humanity with her role in the larger conflict.

The second arc, "Lost in the Cruel World," shifts focus to Mikasa Ackerman. This arc presents an alternate reality where Mikasa imagines a life without Eren Yeager. In this scenario, Mikasa is raised by her biological parents, living a peaceful existence until tragedy strikes. The story examines Mikasa’s deep emotional ties to Eren and how her identity and sense of purpose are intrinsically linked to him. Through this alternate timeline, the narrative explores themes of loss, identity, and the fragility of human connections.

Both arcs provide character-driven narratives that complement the main series by offering a more intimate look at Annie and Mikasa. The stories are grounded in the psychological and emotional dimensions of their experiences, shedding light on their personalities and the choices they make. The manga maintains the tone and themes of the original series while focusing on the personal journeys of these two characters, enriching the broader "Attack on Titan" universe.