Ascension of the Reaper

The greatest identity copier in the underworld took one last contract before retirement: impersonate Kaojin, a dead young man from a minor clan, long enough to marry a woman from a powerful family. But on his wedding night, expecting he had successfully finished the mission, he was killed and left for dead. Dying. The only conclusion. But the Reaper itself failed to extract his soul and became bound with him instead, reborn several months earlier as... Kaojin. Feed me souls and you get stronger. Feed me not, and I will eat your soul instead.