Age: At-Least 1000
Hair Color: Black
Eye Color: Black

Sonju (or Sung-Joo) is a demon that lives outside Grace Field House.

He saved Ray just before he was captured by his demon-hound pursuers. He and Mujika were suspected to be demons by Ray.
Sonju believes in the same religion as Mujika, hence is strongly against the practice of eating humans. However, Sonju remained reluctant and was eager to resume his intention of eating humans once their population increased.

Sonju retains a stoic and composed personality, as he sometimes refrained himself from interacting with the orphans, and during the times when he does, he was known to intimidate them due to his appearance. Nevertheless, Sonju on a certain degree still care for the orphans' safety and have faith in them being able to break the promise.