The Tree of Death: Yomotsuhegui 1.

Police officer Nawa Kanetsugu lost almost everything when his wife and daughter were killed. All that remains now is his thirst for vengeance and hunger for the fruit of immortality! But when he takes a bite, he is plunged into the midst of an endless war between the enigmatic and twisted Undying, and Ren, a single shinigami looking to restore death to the world! Can Kanetsugu survive? Of course his body shall—but will his soul?