The idea came to me after learning about the process, sometimes known as detransformation, that bodybuilders go through at the end of their careers that involves diet and workout routines designed to safely break down their excessive muscle mass.
The idea is that the "World's Strongest Woman" naturally blessed with preternatural strength, size, and beauty, which she has honed through judicious training, in her prime, to choose to willingly undergo a regimen of detransformation after badly injuring her boyfriend/fiance during sex.
The story would focus on the changing relationship between herself, her body, and her significant other as she gradually loses her statuesque physique, and the confidence that came with it, and becomes comfortable in a more submissive role while her amazon obsessed boyfriend learns to accept his dream girl turning into a pumpkin and taking the lead in their relationship.