Tegami Bachi by Hiroyuki Asada
In Amberground the only light comes from the artificial sun that hangs over the capital city. The rest of the land is covered in darkness and people are clustered in towns spread out over the land. The only people who regularly travel between the towns are Letter Bees. Named Letter Bees because they normally deliver messages. Think hero mailmen. Yep, that's right, the mailmen are the heroes. And they are awesome. Because in the darkness between the towns are giant armored insects known as Gaichuu. One Letter Bee, Gauche Suede, has been given a strange package to deliver. He has to deliver Lag Seeing, a small boy, to a distant relative. Lag would much rather go searching for his kidnapped mother than have anything to do with Gauche, and he keeps running away. Right into the Gaichuu. And so begins Tegami Bachi.
The are several things I really like about this manga. There is a nice balance between artwork and storytelling. Hiroyuki Asada draws and writes Tegami Bachi and instead of the artwork overpowering the weak story and carrying the manga, here the two actually work together. And because of this, the world of Amberground actually makes sense. The land is covered in darkness, but there are farms, and everything isn't frozen over and Asada has a completely reasonable explanation for why that makes sense in the world or the manga. The combat is fun to watch and Lag and Guache arguing is funny. The manga reminds me a lot of Full Metal Alchemist. The relationships feel similar and the pattern of tension and serious story line broken up by humor and shenanigans is spot on. Thoroughly enjoyable. Go read it now.