The following contains spoilers for the first two episodes of Obi-Wan Kenobi, now available on Disney+.
In the Star Wars Universe, when the cartoons and comics dissected the Inquisitors, it became clear Palpatine had a lot of ways to safeguard his Empire. He eventually handed off their governance to Darth Vader, mandating this sinister legion had free rein to do whatever they needed to ensure his iron grip on the galaxy got maintained. And as expected, Vader drilled them, requiring nothing less than perfection.
That is what the Grand Inquisitor, not just in Rebels years later but in the first two episodes of Obi-Wan Kenobi, demanded as they hunted "old Ben." However, while many thought the Grand Inquisitor would be Vader's deadliest agent, Reva, aka the Third Sister, proved that mantle belonged to her.
Now, that isn't to knock the Grand Inquisitor or even Sun Kang's Fifth Brother because they were pretty intimidating. But Reva possesses something other than Force telekinesis or the ability to use the dark side to mind-probe the likes of Haja to get her way -- she has knowledge. And as fans know, knowledge is the real currency of the galaxy, especially in stories like Obi-Wan Kenobi that have so many secrets.
It was confirmed when Reva confronted Obi-Wan in a hangar on Daiyu in the second episode, condemning him and loudly reiterating she wanted to bring him back to Lord Vader. But as he hid out, Reva dropped a bombshell, admitting Anakin Skywalker was alive and that he was Vader himself. That shook Obi-Wan to end the episode, leaving the former Jedi Master steeped in panic and anxiety because he thought his former apprentice died after being burned on Mustafar.
So, when Reva does get Obi-Wan one-on-one, she can weaponize this info, disarm the warrior with it and attain the prize for her boss. Admittedly, this intel is a major and cerebral trump card, and it will only add to her feisty arsenal. Reva's already cut people's limbs off in broad daylight on Tatooine, and she stabbed the Grand Inquisitor and left him for dead, meaning she's not prone to holding back.
Thus, it's easy to see her getting nasty as she hunts and teases Obi-Wan over his failures with his former Padawan. The fact she green-lit Leia's kidnapping as bait says it all. It makes Reva the perfect mental and physical threat -- a watchdog who Vader wouldn't mind crossing the line to get results. In fact, whether as Anakin or Vader, the Sith Lord has done the same. It's unclear if she alone knows this secret and if Vader has endorsed her, but ultimately, Reva's the ideal predator for an emotionally-broken Obi-Wan.
To see Reva continue her mission, Obi-Wan Kenobi releases new episodes Wednesdays on Disney+.