Sonson J. (ソンソンJ, Sonson Jei) also known as the Bloodthirsty Killer of Emerald Lake was an evil human.
Sonson wears a t-shirt, with "13th" printed in red both on the upper left of the front and the entire back of the shirt, paired with dark pants. His face is never seen as it is always covered by a brown paper bag, with roughly cut-out eye holes. He also appears holding a large knife with blade facing downwards, both features add to his serial killer appearence. This kind of knife is known as a machete.
Not much is known of Sonson's personality but he is shown to be extremely bloodthirsty and shows no remorse at all for his victims, even going as far as to complain that it's disgusting and not fair that only Demon Weapons and their Meisters get to kill as much as they want.
Maka and Soul were assigned to Florence to hunt down his soul as an extra assignment. After Maka lists his felony, he sobs about Meisters and Demon Weapons being free to kill as much as they please. Maka easily cuts him in two and states that it's not true that they are doing whatever they want.
- Sonson J. could be seen as a parody of Jason Voorhees, the famous serial killer from the slasher film series Friday the 13th.
- Sonson has "13th" printed on his shirt.
- Sonson J. is referred to by the title "Bloodthirsty Killer of Emerald Lake", a reference to Camp Crystal Lake, the prime location where the Friday the 13th films take place.
- He wields a machete, which is often seen as Jason's iconic killing weapon.
- The mask that Sonson J. is a reference to Jason's mask in Friday the 13th Part 2, where he doesn't wear his iconic hockey mask.