Black thing under Mesos?

[youtube]thm6szyj3wE[/youtube]
At the VERY beginning of the video, his Item Inventory is open, and you can see a black thing under the Meso Display.
What is it? D:

Pachinko/monster arcade Balls.
(Pachinko is the name if the game itself, though it is called monster arcade. The balls are bought in the CS.)