The monsters were created when an area was thick with negative emotions that created a dangerous byproduct called malevolence. When Seraphim became too connected to a human, seeing their friend physically and mentally turn into a monster caused them to despair and their ephemeral forms were quickly turned into monsters as well.
There were thousands of Seraphim, but mankind was awash with terrible emotions, and could easily be overcome and turn into monsters. The Seraphim have magical powers and their own element to control. The humans prayed to the Seraphim, and in return the Seraphim blessed them.
Humans and Seraphim used to live together in harmony thousands of years ago. Tales of Zestiria the X takes place in a world where there are beings called Seraphim.
