nipple fuck is possible but with limits, 1. If breast size is flat or too small won't fit, 2. Breasts suppose to be the biggest size possible like cup j or bigger, on character creation there would be a "breasts (with womb)" option that can give females, shemales and herms thicker, fatter breasts with big, flexible, stretchy nipples. Different from vanilla types but fit for nipple sex perfectly.