In the land of Amberground, an artificial sun serves as the only source of light for the capital city of Akatsuki while an eternal night persists. The further away one is from the capital, the darker and more dangerous it is. In the surrounding areas of Yuusari and Yodaka exist enormous armored bug creatures called Gaichuu that prey on people's hearts. Despite this, it is the duty of Letter Bees, a special group of mail carriers, to deliver letters throughout Amberground while risking their lives battling the Gaichuu.

Twelve-year-old Lag Seeing aspires to become a Letter Bee like Gauche Suede after their fateful meeting five years ago, where Gauche "delivered" Lag himself as a letter sent by his missing mother. Determined to see Gauche again and uncover the truth behind his mother's disappearance, Lag begins his journey to become a Letter Bee.

Tegamibachi was published in English as Tegami Bachi: Letter Bee by VIZ Media under the Shonen Jump imprint from September 1, 2009 to March 7, 2017. It started serialization in the March 2009 issue of their monthly Shounen Jump anthology. In Europe, the series has been licensed in Italy by Panini Comics under their Planet Manga division, Kana in France, and Planeta DeAgostini in Spain.