Its strange that Kamon never once have Rin penetrate her or anything. she doesnt know yet about the stigma and yet whenever she ever has her hands on him, and actually got him cornered she never sticks it in. Why? Or maybe she learned from that Lisa portugese nurse about the effects of the birthmark?
Also Dad seems to know more how to use the stigma. he may be the one who removed the curse from the other girls without Rin's intervention.