Alternatively, a Token Good Teammate in a team of Villain Protagonists, in other words a genuinely good guy is siding with the protagonists even though they're evil as opposed to fighting against them.
Officer Alice seems to be pursuing Bob for perfectly legitimate reasons, but she's actually a Dirty Cop.
Double Subverted: It later turns out she isn't dirty. Maybe a bit rough at times, but she's still fighting for a noble cause.
Parodied: Alice is such a loveable Wide-Eyed Idealist that Bob feels bad about having to trounce her every time, and usually lets her get a token victory here or there.
Zig Zagged: Alice is a very complex character; she has enough Pet the Dog moments to make it clear she's not evil, but she occasionally does things that could be seen as either Shoot the Dog or Kick the Dog.
Averted: Alice is the antagonist because she's not a nice person.
Enforced: Although the work is about a Gentleman Thief, the writers didn't want to offend the police, and so made their side sympathetic.
Lampshaded: "Me and Alice could have been good friends if we weren't on completely different sides."
Invoked: "Don't make yourself out to be Robin Hood, Bob. You're a thief. You steal from innocent, hard-working people like it's some sort of game, and now you want to pretend I'm the bad guy for trying to bring you in? The hell with that. I'm a cop. I'm here to protect people from assholes like you."
Discussed: "Ya know, Charlie, even though Alice tries to stop me every time I make a big heist, I don't think she's so bad. At least, she's no worse as a person than you or me."
Conversed: "Ever get the feeling we're cheering for the wrong guy?"
Deconstructed: The fact that his nemesis is such a good person makes Bob question what he's doing. He eventually abandons his lifestyle and turns himself in.
Reconstructed: Bob enjoys what he does, or firmly believes it is absolutely necessary. He tries to entice Alice to join his side at every opportunity, and goes out of his way to avoid hurting her, but in the end, they're just two people fighting for what's right...even if it means fighting each other.