The thieves we’ve seen so far have tended to be confident, reckless, anti-hero personality types. In fact, the class’s morality (so far) seems to be a bit hazy. In their sessions, Thieves are powerful and game-changing but also a source of controversy. They delight in stirring up trouble, but sometimes they really do mean well.
Hope is a very mysterious and powerful Aspect. It seems to run on belief - steamrolling all natural laws with the power of wanting something to happen. Thieves steal their Aspect from others and take it for themselves. So what does it mean to steal Hope?
A Thief of Hope might be able to steal others’ belief. This sounds lame, but a lot of SBURB power mechanics rests on confidence in yourself. This classpect might be able to hamstring other players by taking away their beliefs in their own power. And, of course, this would grant the Thief even greater control over their own abilities.
After Vriska steals her opponent’s luck, she’s able to weaponize it against them. A Thief of Hope might be able to manifest the white-light Hope attacks seen from Eridan and Jake if they stole enough Hope from others.
Of course, these are all pretty sketchy actions (which thieves are not averse to). Is it possible for a Thief to cooperate with their teammates?
Well, hopefully we’ll get more insight on the potentials of Thieves and a clearer picture of Hope later in the comic. I don’t think any Class is strictly negative, although some do have leanings. (Princes, which I’ve also been charged with writing on, are unfortunately dealt a bad hand of cards.) A Thief of Hope might be able to steal the motivation or power from enemies. Depending on exactly how tied together Hope and existence/reality are, they might even be able to make opponents pop out of existence! (This seems very Voidy, but consider that Jake and Roxy both were able to summon pumpkins out of thin air. Void and Hope have some connections.)
Again, until we know more, this is what I can offer.