The player's personality is measured by Corruption. Particularly high (75+) or low (25-) will automatically move your personality type, but certain events can also trigger movement on the scale. If your Corruption score moves within the 26-74 zone, it won't change your personality type (though specific corruption gates can impact individual scenes at the author's discretion).
The Dark Knight: High corruption brings in dialogue that is much more selfish, hedonistic, and aggressive(ly sexual). You don't mind stepping on others to get what you want, and nothing matters more than your own pleasure. The Dark Knight has little empathy for others or care for their desires. A mix of Brute and Hard from TiTS.
Please for the love of God don't make it Corrupt = Domme, Pure = Subby. A corrupt submissive or a pure dominant should be just as possible; Corruption is more about whose needs come first, consent, and empathy. A corrupt PC gleefully demands others do what's uncomfortable for them, even if that's power-bottoming an NPC into throwing the PC over the edge of the bed and railing her until she's a cummy mess.
Champion: Low corruption is not necessarily chaste, but is compassionate and good-natured, much like the "Kind" of TiTS, though they may have a slight snarky streak. Champion PCs are more eager to help people, even at a cost to themselves, and are more willing to engage with lovers in mutually-beneficial ways rather than demanding their needs be met first and foremost.
Bimbo. A feminine, cum-hungry sex addict with a vapid vocabulary and an incredible lust, but also empathetic and fun-loving. Bimbos are a middle ground, as sex-fueled as Corrupt PCs are, but much more about taking pleasure whenever and however they can get it: they don't need to get people to do what they don't want to; the Bimbo wants to do whatever they want to instead!
The Bimbo personality overrides Corrupt/Pure in many situations. It's removed either by moving past an alignment barrier, or by specific actions or items that clear it. Bimboism isn't a curse you can't get rid of (by default...), but it's not easy either.
Bimbo is feminine-gated (ie, female, herm, shemale only). Any TF/event that needs to impart Bimbo also needs to shift/lock femininity.