Kuro and Shiro

Kuro and Shiro (クロとシロ, Kuro to Shiro), also known as Doku and Kuro (ドクとクロ, Doku to Kuro) are two skull-shaped beings in Black Rock-chan.

Description
The two beings mainly differ by the upper section of their eyes: one has its eyes sloped inwards, and the other's are more rounded overall. However, it is not explicit which of the two skulls is Kuro or Shiro.

Kuro and Shiro often accompany Decchan or Rock-chan, and they are able to communicate with the latter to an extent. The two are also capable of showing a variety of expressions.

Trivia

 * The names "kuro" and "shiro" mean "black" and "white" respectively in Japanese.
 * The alternate names "doku" and "kuro" can combine together as "dokuro", which means "skull" in Japanese.