Fushi no Sougishi

This is the story of the hero who must kill the princess. In this world, the dead are sent to their final resting places by the Immortal Undertakers, a race of long-living, human-like beings. Leon, a half-breed, is the youngest of them and is on his way to take his final test when his train derails. He meets a human girl in the forest, and though he doesn’t know her, he somehow feels he must protect her…from the other Undertakers!

(Source: Mangamo)