"School-Live! Letters" is a spin-off manga series that expands on the world of the original "School-Live!" story. The narrative centers on a group of students who are part of the School Living Club, a unique organization that operates within a high school setting. The club’s primary purpose is to ensure the survival and well-being of its members in a post-apocalyptic world overrun by zombies. The story alternates between moments of lighthearted camaraderie and the grim realities of their situation, creating a balance between slice-of-life elements and survival horror.

The main characters include Yuki Takeya, a cheerful and optimistic girl who often retreats into delusions to cope with the harsh reality; Kurumi Ebisuzawa, a pragmatic and resourceful member who wields a shovel as her weapon of choice; Yuuri Wakasa, the responsible and nurturing leader of the group; and Miki Naoki, a newcomer who struggles to adapt to the group’s dynamics and the horrors of their environment. The series also introduces additional characters, such as Megumi Sakura, a teacher who plays a significant role in the group’s survival and emotional support.

The plot unfolds through a series of letters written by the characters, providing insight into their thoughts, emotions, and experiences. These letters serve as a narrative device to explore the psychological toll of their circumstances, as well as their bonds of friendship and resilience. The story delves into themes of hope, loss, and the human capacity to endure in the face of overwhelming adversity. While the original series focuses on the immediate struggles of the School Living Club, "School-Live! Letters" offers a more introspective look at the characters’ inner lives, expanding on their backstories and motivations.

The manga maintains a neutral tone, neither glorifying nor sensationalizing the horror elements. Instead, it emphasizes the characters’ humanity and their efforts to maintain a sense of normalcy amidst chaos. The interplay between the mundane and the extraordinary is a recurring motif, highlighting the contrast between their school life routines and the constant threat of danger. "School-Live! Letters" serves as a companion piece to the main series, enriching the narrative by providing deeper context and emotional depth to the characters and their journey.