Very nice of you to propose this.
What do you think of a female character using a mental IQ loss device on a rival to transform her into a bimbo. The trick being that the device also prevent the victim from realising something's wrong, and alter the memories of everyone else/alter reality so that the victim is thought to always have been that way.
The woman is delicted as her rival slowly turn into a bimbo, being the only one remembering her as a competent inteligent woman, gloating in her victory.
Later, as she take a nap or relaxing bath or something else lowering even further her guard, she's unaware of the newly made bimbo finding the device and accidentaly firing it up at her. The bimbo didn't do it for revenge or anything, not being even conscious of having been wronged. It's just a pure accident, a random twist of fate.
In progressive spurts, the woman also become a bimbo, completely unaware of it, until she's wondering why she was, like, feeling so happy moment before? Something to do with her bestie, maybe?
The story end as some other people find the device , wondering what it is, disregarding the idea that it could belong to the two womens. It look way too complex for these two notorious bimbos.
The End.
What do you think of it? :]
I f you don't like it or don't feel inspired about such a plot, no problem!