Darkness covered his heart.

He was searching for something in the dark.

He was searching for something in the darkness.

It is said that terrifying creatures live in that dark forest.

His heart seemed as dark as pitch.

He borrowed a large amount of money from a loan shark and is struggling to repay it.

I'm planning to have a potluck party with my friends tonight.

As for his future, it's unpredictable.

He said '一瞬先は闇', explaining that predicting the future is difficult.