Yami Baito Saki wa Isekai Deshita

A high school student named Hashiba Ryuuji must abandon his personal aspirations after his parent becomes seriously ill, forcing him to seek employment to cover medical expenses. He discovers a part-time job offering unusually high pay and, despite his doubts, accepts the position. Upon following the employer's directions, he goes through a strange door and is transported to an unfamiliar world, where he is immediately attacked by monsters.