Was there a novel in which the main character was a sealed demon king who was a collection of dark energy, and the title and other details had been forgotten?

The main character was a demon king, a collection of dark energy. He was immortal and could only be sealed.
The main character had a few subordinates, but those subordinates didn't listen to the main character's words... The tragic demon king.
The main character was a collection of dark energy, so he would not die and could only be sealed.
At the beginning of the novel, the protagonist lost almost all his strength, and his only subordinate was a cockroach.
There was also a transmigrator who was extremely unlucky. He even obtained a plaque from a place called the Wind Continent that said,"The World's Most Unlucky".

Answer 1

I recommend you to watch the Immortal Witch. The main character was an Earthling who transmigrated to another world and worked hard to become immortal. Among them, the main character type was the wizard type, and he was decisive in killing. Although the main character doesn't fit the description of " dark energy," the main character doesn't die. At the same time, the book also contains dark elements. Perhaps you will like this novel. I hope you like my recommendation.😗