Solo bad endings. The "Encourage" prompt won't appear until all 3 have been completed. To get a solo bad ending, the girl of your choosing must be rehabilitated first, but only 5 or 6 times of the 9 total rehab sessions.
More than that will get you stuck on the good ending branch. Less than and you run the risk of unlocking another girl's bad ending, depending on who was rehabilitated last the most often.