[rick404]

I definitely prefer some aspect of a physical change as mentioned, however, the main key is personality change where the character is acting independently out of their own (altered) free-will.

So figure a few examples...
Innocent to Wanton/Lustful
Noble Heroic to Power-hunger killer or Righteous to Demonic.

To me this aspect goes beyond simply mind control and brainwashing.

Mind control often uses some form of external device be it a spell or machine that forces the character to act according to the will or the operator. So the character isn't really acting on their own.

Brainwashing is like training, or simply making a character identify with the captor, and is often connected with some sort of reward or punishment. Which doesn't strike me as total free-will.

So going for simply a change from 'good' personality to an 'evil' one simply a change in the characters expression, clothing, or action is enough to satisfy. Such as the 'naughty look' used by Crooked Navel, Snowolfyue, or in the Yame no Koe games.

However, in order to really make it work you need an established character, a detailed process, and typically a reaction of the changed character and her former comrades.

Body modification TF of course make it all the more entertaining adding a more dramatic contrast to the before and after.