I Reincarnated as the Monster That Killed Me by Angel Pena

I Reincarnated as the Monster That Killed Me follows Alkaios, a nineteen-year-old bell-caster who dies when a supernatural calamity called the Sorrow destroys his village and kills his family. But death is not the end of his story. Alkaios awakens three days later in the body of the very monster responsible for the massacre—a young, hound-sized vessel of an ancient creature that feeds on grief.

Guided by the consciousness of Aristion, a former host trapped within the monster's marrow, Alkaios discovers that the Sorrow does not simply consume flesh: it feeds on grief, fear, and the sorrow left behind by death. To preserve his human identity, he must learn to survive by feeding only on the grief of the long dead while resisting the creature's hunger for fresh suffering.

Meanwhile, Athanasia, the sole survivor of Hollenmere, joins the Cindersworn, an order of hunters dedicated to destroying calamities. Carrying the little bell that once belonged to Alkaios's sister, she vows to discover the monster's true name and destroy it.

As Alkaios slowly grows in power, he faces an impossible conflict: the monster he has become is the very creature he swore to hate—and the survivor hunting him is someone he once loved.