MacGuffin

A small black flat rock considered by the Bureau as the source of the abilities in Sakurada.

Some people try to get the MacGuffin because of it's supposed power. Despite this, the Bureau does not seem to care much about it.

Trivia

 * In fiction, a MacGuffin, is a plot device in the form of some goal, desired object, or other motivator that the protagonist pursues, often with little or no narrative explanation.