Letter Bee is one of those series where the anime was pretty good, the original ending was even decent, but as soon as I read past the point where the anime and the manga diverged I was unhappy that the anime hadn't gone the same way. Again, the anime is hardly bad and I think above average, but the manga is just superior in terms of storytelling and tearjerker moments (thank you Viz for licensing it).
Letter Bee (Tegami Bachi) by Hiroyuki Asada
In the land of Amberground, there is no sun and only the elite who live in the capital of Akatsuki get the full light of the artificial sun, for residents of the farthest regions the sun is never brighter than the full moon. And not only are people restricted from crossing between areas of Amberground but Gaichuu, giant metal bugs, attack anyone who dares to travel and eat their hearts which makes being a postal carrier (a Letter Bee) the most dangerous job in the country since they carry people's hearts in their letters. Lag Seeing has just become a bee after being inspired by Gauche Suede, a bee who delivered him when he was a child, and is crushed to discover that Gauche disappeared years ago and no one knows where he is or even why he vanished. Despite all of this the manga manages to be upbeat and heartwarming at many parts, even when more and more of the backstory comes to light, and, as strange as it sounds, I love how this manga almost makes me cry so often. By this point it's hard to tell who is going to live, who's on what side (never mind their motivation) so, even though I do believe the story will have a good ending, I have no clue how it's going to get there or what is going to be sacrificed for it.