"Letter Bee: Light and Blue Night Fantasy" is a two-episode anime OVA that serves as a prequel to the main "Letter Bee" series, offering insight into the world and characters. The story is set in the land of Amberground, a world perpetually shrouded in darkness, where artificial sunlight is provided by a man-made star called the "Spirit Amber." The narrative centers on the profession of Letter Bees, couriers who deliver letters and packages across dangerous terrains, often facing threats from Gaichuu, monstrous creatures that inhabit the darkness.

The protagonist, Lag Seeing, is a young boy who aspires to become a Letter Bee. Lag's journey begins when he is entrusted with a special delivery by Gauche Suede, a seasoned Letter Bee who rescues him from a perilous situation. Gauche becomes a mentor figure to Lag, instilling in him the values of courage, determination, and the importance of delivering messages that carry people's hearts and emotions. The OVA explores Lag's early experiences as he learns the ropes of the profession, highlighting his unwavering resolve and the challenges he faces in a world where light is scarce and danger is ever-present.

The plot delves into the bond between Lag and his Dingo, Niche, a mysterious girl with a tail who possesses extraordinary strength and serves as his protector. Their partnership is central to the story, showcasing the trust and camaraderie required to navigate Amberground's treacherous landscapes. The OVA also introduces key themes of hope, connection, and the transformative power of letters, which serve as lifelines for the isolated communities of Amberground.

Through its concise narrative, "Letter Bee: Light and Blue Night Fantasy" provides a foundational understanding of the series' world-building and character dynamics. It sets the stage for Lag's growth as a Letter Bee and his eventual quest to uncover the mysteries of Amberground, including the fate of Gauche Suede, whose disappearance becomes a driving force in the main series. The OVA effectively captures the emotional depth and adventurous spirit that define the "Letter Bee" universe.