Jack

Jack (ジャック Jakku) is the spirit of a murderer and Matilda Matisse's guardian ghost.

About
Jack was once a killer that lived in London in the early 20th century. His method of operation was so atrocious that Scotland Yard decided to keep his case a secret. Jack had a gentle personality but one could see the madness in his eyes and he became known as the "Second Jack". He had already killed 112 people, including his own family, when he himself was shot down when he tried to attack a policeman.

But his spirit lingered within his knifes. He was eventually sealed by the witch taking care of Matilda Matisse, but once she died the seal was removed and though Matilda knew he was dangerous, she still took him as her guardian ghost.

O.S. Jack The Ripper
O.S. Jack The Ripper (O.S. 切り裂きジャック) Description: The medium was made by Matilda herself, using a real pumpkin head and tin for the body. The O.S. was made to perform fast surprise attacks and the opponent would only notice the attack once it has been stabbed. The knives are polished by the oversoul to be able to cut anything.
 * Shaman: Matilda Matisse
 * O.S. Type: Spirit Type
 * Spirit Ally: Jack
 * Medium used: Pumpkin Doll

Attacks
 * Trick or Treat (トリック・オア・トリート Torikku Oa Torīto): Jack runs toward the opponent, opens his chest, and tries to capture and shred the opponent inside him.
 * Slice and Dice: Used to break Horohoro's ice attack.
 * Halloween Twister: Jack spins around his body along with his blade to hit the opponent several times.
 * Death Scythe: Jack delivers a powerful downwards slice.
 * Pumpkin Dumpkin: Jack throws his pumpkin head at enemies.
 * Nightmare: It makes the enemy see nightmares when they are asleep.
 * Pumpkin Eater: Jack stirs up a hurricane that engulfs the enemy.

Anime/Manga Difference
In the anime after Matilda is given an extra furyoku power boost from Asakura Hao, she creates a new massive Over Soul with Jack. It takes the shape of a big scarecrow with a very large pumpkin head while using a scythe, but it is easily defeated by Asakura Yoh.