心中天網島 is based on a 1721 文楽 [#bunraku] puppet theatre play]. As traditional in this style of theatre, the puppeteers are in full view of the audience wearing all-black cloaks. 心中天網島 does the same, but substitutes the puppets with flesh and blood actors.

 

The puppeteers are 黒衣 [kuroko, litt. “black clad”, though there are colour variations depending on the scene's requirements], guiding the performers towards their destiny.