you have been kicked out by your family and have nowhere to live

you go and see Step-Aunty and beg Her to let you stay with Her

She only has one reservation, She doesn't like boys, AT ALL

So, if you stay you will have to become Her Step-Niece and do exactly what She says

you are desperate and accept Her offer

She strips you and starts dressing you up as a frilly pink sissy and tells you how She is now completely in charge