Disclaimer: Don't own it. Don't sue me.
Spoilers: Sort of for Kill Ari.
She had been surprised, to say the least, when Gibbs asked her to back him up. Surprised that he could trust her, after all, she worked for Mossad, and Mossad was backing Ari. And screw impartiality, she was backing Ari too. She found it impossible to believe that her brother had done everything that they had claimed. Ari who wanted to help people, Ari who wanted to make a difference. Ari and Tali, her better angels. This was all one massive mess. Ari was a little dark, maybe. Hurt, haunted . . . but the job did that to a person. Ziva had experienced her share of pain. Memories that would never leave her, no matter how much she might want it. And Ari had been at it for longer, been through more. But it always seemed to be Ari who saved her. Always. He was her protector. Since childhood, it had always been that way. Even when she could protect herself, and especially when she couldn't. She owed him her life more times than she could count, and her sanity a few times more. Her perfect big brother, who all her friends had envied. But he had looked out for them too, because what was important to Ziva was important to him.
She remembered with perfect clarity the day Tali died. The day she might have died too. She and her little sister were shopping, taking the rare opportunity just to be two young girls. Ari had laughed at their enthusiasm, and hung back somewhat, but they had both known he was keeping an eye, and it made them feel, well, safe. Tali, in her eagerness, had ran into a shop and Ziva, amused, had taken off on her heels. The force of the blast blew her backwards, and she was knocked out. She had woken to Ari pulling rubble off of her. He seemed bruised, he'd probably been thrown back too, but the real pain was in his eyes. She had choked out the question – just Tali's name, she couldn't say any more, and Ari had shook his head slowly. Looking back, it was probably the last time she saw him cry.
She watched the two men verbally sparring down in the basement; saw what had become of her older brother. He may have just been pretending, or something, but the callous cruelty still shocked her. Surely this wasn't Ari.
"I've killed enough men in my life. It's gonna be just sweet watching you die."
"Ari, please don't."
Her voice, though barely audible, shocked herself. This was a decision she knew she would have to make, and she knew what to do. She just didn't want him to die.
"I'm sorry to spoil your fun."
The gunshot sounded louder than any explosion. Reluctant tears welled in her eyes as she descended the stairs. A few rolled down her cheeks, but she wiped them away angrily. She looked at the body for a while, and then turned to the other person in the room, feeling excruciatingly guilty. He walked up to her and she dropped her head onto his chest. The two stood in silence. Finally, he said,
"It's done, Ziva."
She'd always loved how her name sounded in her brother's British accent.
Please don't kill me.