Hai Shinigami to Fushi no Neko

In the Republic of Enetia, a maritime nation dealing with the spread of the black disease, a state-sanctioned assassin named Gatto aspires to become a top enforcer of justice. After a failed mission results in his reprimand, Gatto witnesses a colleague's death and transformation into a puppet. This shocking incident prompts him to encounter a mysterious figure who identifies as a death god.