Zankoku na Imomushi no Tsubushikata

A story about boys who want to become a girls and a beautiful doctor.
It's said this legendary female doctor gives handsome boys sex change operations for free.
Instead, her fee is tormenting the boys and giving them pain.
If they can hold on 'til the very end, she'll make them the girls that they hope to become.

[From DLsite English]