In her school, Milky is a member of the health committee. So when her friend asks for help with getting credit for her health class, she’s happy to help. To get credit, she needs to watch a training video (starring Milky) buck naked and then provide material proof that she watched it (her own semen).
A common friend joins in as moral support, but when three futanari girls are half naked in a room together, stuff tends to happen.