Shimai Ijiri

Two sisters are orphaned, their parents left them only debts, in order to pay them and get themselves a comfortable life, they have to become slaves for a dark organization, and they begin their training under the guide of a man who uses words and reasoning as his only tools, and he is determined to make them the perfect slaves, if he succeds, he will be able to retire from that organization.
(Source: Anime News Network)