After reading Sarada's text,  Kasai laughed with Orochimaru.

"It's time granny. I will meet her as she requested.  Hahaha.."  She waived goodbye to Orochimaru.

"Little did she know...  This will be the first and last day she has the mangekyo." Orochimaru smiled.

"I will call you when I am done with her." She smiled back.
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Time skip
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Sarada excitedly went to their rendezvous. But she was shocked when Kasai faced her with full mangekyo. She looked like she's ready to kill her.

Sarada was nervous at how Kasai looked at her. She had never seen her like that.

"W-whats wrong sis? " She asked.

"Take this Sarada." Kasai choked her neck as she concentrated her chakra on her palm producing chidori.

Kasai changed the chidori pattern to allow its current to flow all over Sarada's body cutting through some of her vital nerves.

Sarada desperately thought,
It's difficult to breath and I felt like I am losing my life. But I cannot die today. I cannot let my sister be a murderer. I have to save myself.

Lord help me pleeaassseee...

"Ka...s..a..i... don't...ple..ase... do...n..'t...." she tried to stop Kasai. While her eyes also turned to mangekyo

Kasai saw her eyes changed to mangekyo. Sarada emitted a little black fire that burned her palms. Kasai's hand is burning from the black flame. She felt excruciating pain from the fire. And she cried.

Sarada felt sorry and guilty for what happen to Kasai.

She calmed down and deactivated the mangekyo. Then the black flames were gone. She didn't know she had acquired the power of amaterasu through her mangekyo.

Hn.  Sarada's mangekyo is able to make the amaterasu! An unquenchable black fire...
It won't stop unless the jutsu is cancelled by the one who casted it. This is one of the eye powers of papa and uncle Itachi.

This time Kasai was smiling. Ha.. her eyes are mine... I am going to have the eternal mangekyo today and have that jutsu. She thought as she cuts Sarada with her sword charged with chidori.

Sarada coughed blood and her abdomen bled as her body suffered from the blade and chidori.

Her thoughts were still denying the situation she is in. She was hurt by her sister and she hurt her too with a strange black fire. It was her first time to see it. She does not know how to control it.

But the pain was tolerable. Kasai had not hit the vital part on her abdomen. She felt a different power within her. Her eyes also felt more superior than before.

Kasai had drawn her sword confident with her great skill in kenjutsu.

Sarada defended herself with her sword too.

I am way behind Kasai in all jutsus but I must survive. She thought.

She saw Kasai's chakra flowed on her sword creating a lightning sword directed towards her. So she dodged it fast.

And again uncontrollably the black fire went out of her system burning the sword of Kasai.

"Wow that's cool!  You got me there. Ha!" Kasai said with sarcasm.

She perceived that although Sarada had the amaterasu  she seemed like she's unaware what that is and how she should used it.

"You're naive Sarada.. You have the amaterasu. Same with papa and uncle Itachi. It's a waste if those eyes be yours idiot! Hahaha.. Don't worry sis, I can make full use of that power. Hihihi..." She laugh and lusted after Sarada's new eye power.

"That will be mine!" she shouted as she released her lightning balls  hitting Sarada.

Sarada knelt on the ground weak and desperate. "S-stop it sis... Why are you doing this?" Sarada asked.

"I-I am s-sorry I hurt you, but must you kill me because of Bolt? "

"Bolt? Do you think this is just because of him?" Kasai smugged. "No... No.. Sarada I hated you from the start!"

"F-from the s-start? B-but you are my sister.  I thought we were ok." Sarada trembled as she felt her chakra was draining.

"I am not your sister. I never thought of you as such. You were nothing but just my eye replacement. I just needed to replace my deteriorating eyes. " She said.

"W-what? " Sarada couldn't believe what she heard.

"I will have your eyes after this fight and I will have the eternal mangekyo." Kasai confessed unpenitent.

Sarada realized how fake Kasai is. "So that was your motive from the start? You were just acting kind and loving to steal my eyes..."

She cried and was depressed of the thought that she was betrayed.

At this point she knew Kasai would be successful. She had only trained for three months. She is nothing compared to Kasai who trained for 15 years with their father.

She just prayed to God for help. She knew she'd end up dead today.  Her nerves were failing her. Her body were chilling. She laid on the ground. Her eyes may have felt very powerful but her body cannot cope up.

As her chakra was fully drained, the seal of the curse mark opened. The power of Orochimaru's curse mark started to take control over her body.

She felt her chakra was replenished. She felt stronger this time. But her soul felt the evil of this power. Her lust for blood is overflowing. She wanted to kill Kasai. It was like another self. She had never known herself as this. It was like the beast inside her was unleashed.

So this was the mark that I had? It gives me a very strong power. Stronger than my normal power. But I felt like I have a strong urge to kill. My reason is leaving me. This beast mode is slowly dominating me. I don't feel like human anymore.

She attacked Kasai with only taijutsu but because it was powered by the curse mark, Kasai obtained heavy injuries.

I am faster and stronger. I am very powerful. I felt so evil within that I am happy with her suffering. Sarada thought.

"I will kill you Kasai." She exclaimed.

Sarada activated her mangekyo and casted amaterasu  targeting Kasai. But it just went through her body. Kasai used her mangekyo to kamui  (transport) her body into another dimension dodging all fire and physical attacks.

This angered Sarada. She turned around and saw Kasai in the same place where she was before their fight even started.

She wondered,  why did she look as if she had not fought with me yet?   What's happening?

As she approached her, the scenario repeated from the start of when Kasai choked her neck. And èverything follows exactly the same sequence until she casted her black fire to her. And when she turned around again, the scene was back from the before they even fought again.

"Hahaha...  Sarada!  You're now under my Izanami. Hahaha... That is a never ending scenario for you idiot!" Kasai declared laughing.

While Sarada was going crazy inside the izanami. Kasai felt the joy of success. She laughed to her heart's content and called out Orochimaru.

"Come out from hiding granny, I know you're  just watching us.. Now is the time for eye transplant." She said glady.

Very good,  Kasai.. You're indeed worthy to be my next vessel. Orochimaru smirked.