Shaman King Zero

Shaman King Zero (“シャーマンキング0) is a series of omake chapters. The chapters are serialized monthly in JumpX magazine. The first chapter was released in November 2011, in volume 5 of the magazine, and will continue until March 2012.

About
The chapters tell early stories of the main characters such as Asakura Yoh, Tao Ren, Usui Horokeu and Lyserg Diethel from the before the main series began.

Source

 * Shaman King Zero at JumpX