Having the burden of taking care of his little sister who is a shut in, Ryo decides for himself to pull an all nighter for the finals exam only to die in the process.
After finding himself in another world in the slaves quarters of a noble household he is determined to find a way to support his mother when his father is too sick to support the family.
He decides to earn his freedom and become an adventurer, but he joins the worst guild and becomes a black company adventurer: the only guild that would accept a slave.
(Black company is referring to the Japanese term associated with exploitative work environment in which work often comes at the cost of ones health)