Throughout the sword of truth series Kahlan's confessor powers seem to work on everyone but Richard, Darken Rahl, and Zedd. Why was Darken Rahl immune to her powers?
Kahlan's ordinary magic is Additive, thus Darken Rahl has protection it from Subtractive side, also due to the fact he has invoked the power of Orden.
Wizard's First Rule Chapter 31
“Does it work on everyone?”
“Everyone human. Except Darken Rahl. The wizards warned me that the magic of Orden protects him from our touch. He has nothing to fear from me.
However, Con-Dar has elements of both. Theoretically, Kahlan could have used it on Darken Rahl.
Wizard's First Rule, chapter 48
The Con Dar is invoked for vengeance. Confessors who invoke it rarely survive; they give their lives over to the goal, give their lives to carry out the vengeance. Kahlan is going to use her power on Darken Rahl.”
Chase stared in shock. “You told me her power can’t touch him, can’t take him.”
“It couldn’t before. I don’t know if it can now, but I doubt it. Nonetheless, she is going to try.
But due to Rahl's scheming,
she used her power on Richard (as was predicted by Shota), who was seen by her as Darken Rahl due to the 'enemy web'.
Thus she did not have a chance to try it. So the question of Darken Rahl's immunity against Con Dar is open.
From what little we see of Kahlan's power "not working", it seems that there is some way to block a confessor's power with the magic of the Underworld. We only see Kahlan use her power three times against someone that does not become Confessed:
- She tries to Confess Demmin Nass and fails; Nass is protected by an "Underworld spell" that also blocked Zedd's magic;
- She tries to Confess Zedd, but his soul was half-trapped in the Underworld at the time; he even uses her power to bring himself back:
(Kahlan:) "Why didn't it change you?"
Zedd straightened his robes, seeming a little embarrassed at his helpless predicament. "Because of where I was." He held his chin up. "And because I'm a wizard of the First Order. I used your Confessor's power as a lifeline, to find my way back."
- At the end of Wizard's First Rule, she tries and fails to Confess
Richard; in this case, he is immune to her power, because he's already unconditionally in love with her, and that is the only defense against her power.
Confessor magic is Additive magic; it would make sense, then, if Darken Rahl is an agent of the Keeper of the Underworld and has access to Subtractive Magic, that he could potentially make himself and his Quads immune to Confessor magic. It must be difficult to do, though, or they wouldn't need Quads in the first place (the whole point of a Quad is that 3 of them will die due to the Confessor), and his Mord-Sith wouldn't be vulnerable to Confessors.