Kotoamatsukami: An ability unique to Shisui's Mangekyou Sharingan. It allows him to impart one command in any given person that they cannot disobey. It's basically the Narutoverse's Geass :3
Speaking of Naruto, I do not own xD
Uchiha Shisui thought that He had seen it all. In his sixteen short years of life, he had seen people kill and be killed; he had taken many lives with his own two hands. He'd seen birth and death, life and destruction, in equal measure. He had witnessed things that would make a normal person's stomach churn. With all the fucked up things he'd gone through, he thought that nothing could surprise him anymore.
Oh, he was so wrong.
He had been in the kitchen, making a cup of chamomile tea to fend off a bout of insomnia, when he heard the door slide open.
How the hell- he locked that door, he was sure of it. He rushed to the door, prepared to fight an intruder. Only it wasn't an intruder.
He looked absolutely awful. His long black hair was disheveled, his face pale and grayish. Dark bruise rings under his eyes attested to many a sleepless night.
"What's going on?" Shisui asked, taking a step forward and holding out his arms, figuring maybe Itachi had just had another bad dream.
Itachi collapsed against him, his entire body trembling.
"Itachi! What's going on?"
"...I can't do it, Nii-sama."
"I can't...Danzo-dono...he wants me to...Nii-san, I can't."
Shisui grabbed Itachi's shoulders and shook him.
"Get a grip, 'Tachi. What the hell's going on?"
And then Itachi spilled his guts on his latest assignment. The more Shisui listened, the more horrified he became. By the end of it, Itachi was shaking and crying so badly that he couldn't speak anymore.
"This...this is awful. What are you gonna do, 'Tachi?"
"I-I d-don't know, Shisui-nii. What can I do? If I do it, then I'd have to kill everyone...but if I don't...I wouldn't be able to live with myself if our clan went through with the coup."
Damned if he did, damned if he didn't. What was a thirteen year old boy to do? To raise a hand against his own clan should have been unthinkable. But, as much as he hated Danzo, he knew that he was right; if the Uchiha revolted, it would start a full-blown world war.
Then, an idea formed in Shisui's mind. He had his Mangekyou, and his new Jutsu. Maybe, if he used it right, he could halt the whole thing in its tracks. The coup d'etat, the massacre...everything.
"Let me talk to Danzo. Then I'll talk to your dad. I think I know what to do."
Itachi snuggled close to his cousin and nodded.
"But Itachi, if this doesn't work, you'll still have to go through with the other plan. Do you think you can do it?"
"...I don't know, Nii-san. They're our clan...I don't think I could."
"It's our clan or our village, Itachi. Which is it gonna be?"
"Itachi, look at me."
Itachi looked up into the four-pronged design of Shisui's Mangekyou Sharingan.
"You have to protect Konoha, no matter what that means, alright?" As he spoke, Itachi's face went blank as the Kotoamatsukami took hold on his mind. "You have to do whatever it takes to keep this war from starting."
When Itachi responded, it felt as though he was detached from his words. Like someone else was speaking through his mouth.
"Yes, Nii-san. I will."
"I swear to God I'll do my best too. But you have to be ready."
Shisui kissed his forehead.
"I'll talk to them first thing tomorrow, alright? Let's have a cup of tea, then we need to get you home. You need to rest, you look awful."
He took Itachi by the hand and led him to the table. In a few moments, he set two steaming cups of tea down, and sat across from his cousin.
"I put a lot of sugar in, just like you like it," Shisui said, with a teasing smile.
"...Thank you," Itachi said flatly.
For helping me. For being there for me. Even though you used the Kotoamatsukami on me...We have to protect the village, no matter what the cost. "For the tea. Thank you, Shisui Nii-san."
"Oh? Yeah, it's nothing."
I'm sorry I had to do this to you. I know you understand.