As the four left the Bronze and headed to the High School, Xander was feeling nervous. What would he say to his psuedosis? I miss you and I'm glad you're not a vampire, was pretty much all he could think of, hoping something else would come to him as they arrived at the school and headed for the library.
"Ah, Buffy, were you able to help Faith?" Giles asked as the four of them entered, he stopped when he saw Xander. "What?"
"I'm not talking to you right now, Giles. I'm too angry, but trust me, we're going to have a long and painful conversation later. Everyone meet Xander Harris, from another reality. Faith made a wish while Angel and I were talking to her, a demon said wish granted and another Xander showed up in a flash of light."
"And what was this wish?" Giles asked.
"That there would be someone in this town that actually gives a damn about me." Faith answered.
Willow stared at her and then the other Xander. "And this demon brought another Xander here? And you actually care about her? Why? She lied about Buffy, she's killing people, she's a monster and a slut!"
"Breath Willow." Local Xander said. "And I still say she had to have a good reason to do that."
"What reason could there possibily be for killing a human?!" Willow demanded.
"He looked like a snake." Faith answered.
"Oh, now you're claiming to be crazy?!"
"She's not, Willow." Xander told her.
"But Buffy didn't see a snake!"
"Because Buffy's can't see what Faith can, or that I can see." Xander addressed the local Xander. "When you look at Angel, what do you see?"
"Something dark and nasty. It makes the hair on the back of my neck stand up and my skin crawl."
"Xander, stop it right now!" Willow ordered. "Stop being mean to Angel!"
"He's not." Faith said. "I feel and see the same thing."
"Buffy doesn't and she's the Slayer, she'd know."
"No she wouldn't, Willow. Her abilities work differently than ours."
"What does that mean?" Giles asked.
"It means we may have been mistaken." Wesley answered. "Faith may not be a Slayer. She's something else and it seems both of the Xanders are as well."
"What? What's wrong with Xander?!" Willow demanded.
"Nothing." Xander answered. "Essentially I'm a naturally occuring version of a Slayer and so is Faith. Where's Uncle Rory?"
"He died a few years ago, something got him. Probably some kind of demon."
"Unlikely, he could handle demons, vamps too. A rogue Wesen probably." And he began to explain.
"That's crazy." Willow insisted. "We would know about stuff like that."
"You do, you just call it fairy tales."
"Hogan Martin took one look at him and practically ran screaming out of the Bronze." Buffy told them. "Amy wasn't afraid of him, but that's because apparently she's capable of being something to be afraid of herself."
"She's a witch, like her mother." Willow said.
"No." Xander said. "She's an inherently magical being. Naturally occurring, like all Wesen and Grimms."
"Xander is not one of them!" Willow insisted, then drew back as Xander's eyes went black and he walked over to his counterpart, who met his eyes.
"Is that - ."
"That is the truth of you, of us. We are the Guardians and when necessary, the Executioners of the Wesen. We are not monsters and neither are they. Amy has agreed to help you learn. Tony is angry and bitter because the family Legacy bypassed him, but not us or Rory or their mother. Sunnydale is our territory and we protect it from all threats, vampire and rogue Wesen alike. We have a purpose, one given to us by nature itself. We see the truth in the dark."
"Buffy, are you sure he isn't some kind of demon?"
"He feels natural and human, Giles. No different than the Xander we know. And yet I saw him lift two grown men who threatened Faith and hold them over his head. I saw him throw Wesley across the room when they tried to grab her, I saw him pull the chains attached to Angel's wall out of the wall. He's easily as strong as I am. And Amy has agreed to help him, she's at the Mansion right now checking the Magic."
"What do you see when you look at Buffy?" Xander asked his counterpart.
"There's something dark in her too, but it doesn't feel evil. What is it?"
"Nothing!" Willow insisted. "There nothing dark to see."
"Um, actually there is." Giles said. "The Slayer Essence, you can really see it?"
"Yes." Both Xanders and Faith responded simultaneously.
"And apparently his group recently discovered the Slayer Essence is power taken from a demon." Buffy glared at Giles. "And my soul may have been damaged by me dying. And with my soul damaged I'm vulnerable to being corrupted, which you conveniently managed not to mention."
"It also seems you have been neglecting your duty to Faith." Wesley said. "There can't be two Slayers in the world, one will be corrupted. We're taught that. Did you neglect her in the hope that she would be the one to be corrupted and not Miss Summers? Is that why you've allowed her to be in a relationship with that creature, because it might help her to manage her darker impulses? Too bad he's under a curse, one it's been predicted that Miss Summers will break. Which would unleash one of the deadliest vampires in history back into the world, because the soul is only caging the demon, not replacing it."
A/N A Grimm's eyes going black is only seen once on the show, I think. Trubel, another Grimm's, eyes go black. It is however described by several Wesen and Monroe explains it to Nick, who had no idea.