The black one is Hibari Kyouya. The white one is like a ghost, a lamp, and a moon.
There is a legend that Hibari Kyouya guarded Namimori because there was a treasure in Namemori that had not been explored.
Later, because the treasure was found and the excavation was completed, there was no money left to dig out.
So he went to Vongola to work as a soldier to make money, and to Milufiore to destroy public property.
There is also a legend that Kito Suigetsu is the person who helps Hibari Kyouya discover treasures.
Its excavation capacity is comparable to that of a dozen excavators, but of course the cost is to lie in a hospital bed for several months.
So based on their abilities, we can build an expedition team called Black and White Impermanence.
-----------------------
Life is a game of backgammon.
The black one goes down first to attack. The white one comes down from behind, for receiving.
Then... Suigetsu was attacked by Hibari. Above