Yami Baito-saki wa Isekai deshita

Synopsis:

Ryuji Hashiba, a high school student, has forced to work and give up his goals in order to acquire the money necessary to cover his mother's hospital bills since she passed away. When Ryuji discovers an incredibly wealthy part-time job one day, he takes it despite knowing it is dubious because he wants to follow his goals once more. Following his employer's orders, he enters a secret door, emerges into an uncharted world, and is then ambushed by monsters...!?