Tegami Bachi

Plot Summary: The world of Amberground is dimly illuminated by a man-made sun above the capital, Akatsuki, but people still send mail past the rivers surrounding the darkened reaches of the country. Postal workers by different ranks deliver everything—packages, parcels, and letters—including Gauche Suede, a reserved letter bee. When Gauche’s letter delivery turns out to be a seven-year-old boy named Lag Seeing, a journey of wits and bonding begin. In embarking on the delivery across plains of snow filled with armored bugs called gaichuu, Gauche has his hands full with keeping both him and Lag alive to complete a life-altering delivery.  (Source: anime3000)