To the people crying NTR. Please do us a favor and stop reading. You are clearly too immature for this type of media.
What part of an organized crime manga did you think was going to be some happy fluffy romcom?
It was spelled out literally during this chapter. The point was to brainwash her into no longer being human. Just a mindless killing machine.
At what point was it even hinted at that he intended to fuck her or do anything of the sort? He wants her to lose her humanity so she can be his ultimate weapon. Seriously grow up people.