A supernatural massacare

--------STILL FLASHBACK-------

The next day a researcher came and took Akira away with him and that was the last time Kuroka or anybody else had seen him.

One week had passed since Akira was taken. In this last week Silvia had cried till her eyes went dry and then some more. Shirone and Kuroka were no better. Akira had always returned after a day he had been taken and then he would come back and cry. Both Kuroka and Akira did not tell them about the experiments so they only knew that Akira and Kuroka go through some training and whereas Kuroka would come back stronger, Akira would come back crying like a wimp.

This is the first time he had been gone for so long and Silvia who had no one else except him is afraid that he would abandon her. Kuroka is too busy guilt tripping herself for failing to protect her little brother to take care of his little sister.

In the following day, Kuroka was taken for another experiment. While gritting her teeth, she endured the usual pain. Still strapped in the experiment table Kuroka was waiting for this to just get over.

Outside the room, researchers looked at the data of the experiment on their computer screen and shook their head. Date on their computer screen showed that her strength had reached the peak at just below ultimate class and her potential had been squeezed dry and their was no hope for her to reach super devil class.

" Sigh! this subject is hopeless there's no need for further experiments on her, master Nebarius will be disappointed again. Anyway start experimentation preparation for white cat. " said the head researcher while looking at the data.

Just then a Man walked toward the researchers ( no description for mobs plz ) and asked in a slightly chilly tone, " how is the progress? is something wrong? "

The head researcher cautiously told " master Nebarius it's like this, the black cat's strength has reached a bottleneck and further experiments on her will only result in failure so we would like to start experimentation on the white cat. " when the researcher said that, the room suddenly turned chilly and everyone couldn't help but shiver.

But that didn't last long because (unknown) Nebarius opened his mouth and asked, " and what about the boy? " Same researcher again said " master it's the same as every other subject. After the organ transplant, subject stopped eating anything and forced feeding resulted in health complications. He has also showed signs of extreme anger and berserk nature so we have confined him and he will go completely mad in 3 days so I suggest disposing him and stop 'that' experiment until we learn more. "

" Hmm how high is his strength? can he be used? " asked Nebarius.

Researcher replied " master his strength is low middle-class devil but his regeneration and toughness is even higher than a Phenex so he can contend with some low high-class devils but using him is impossible because he will completely lose cognition in a few days and will even attack allies."

While they were talking, Kuroka was also led out of the experimentation room and was being led by two devils that was when she saw her master that she hated to the core came towards her followed by some researchers.

" YOOUUU where is Akira? what did you do to him? " yelled Kuroka with absolute rage.

The footsteps of Nebarius halted along with the researchers. Everyone was looking at Kuroka in horror because she dared to raise her voice in front of their master but Nebarius only smirked in amusement and said " That trash? unfortunately he couldn't even be a little useful and is currently waiting for his death ".

" YOU BAS-- Uggh " Kuroka couldn't finish her sentence as she felt a heavy punch land in her stomach which caused her to choke.

Nebarius leaned in front of her ear and said " failed trashes like you has no right to talk to me much less raise their voice against me. The only reason I haven't killed you yet is because you have some uses left for me. You can also pray that your sister doesn't turn out as much as a failure as you otherwise it'd be a shame "

After saying that Nebarius started walking away while Kuroka thought in her heart ' failure.....trash.... experiment on Shirone.....No..... Can't let..... Absolutely..... Not.....NEVER...BASTARD.....'

Nebarius steps suddenly slowed down and he said in a loud voice " I was going to let the boy live for a few more days before disposing him but now I've changed my mind I'm going to kill him myself ".

Hearing this, the last straw of reasoning broke in Kuroka ' he's going to Kill Akira Torture Shirone and Silvia That BASTARD I'm going to kill him '

Suddenly the air around Kuroka stagnated and became heavy and black miasma started leaking out of her and tainted hellish chakra started gathering around her and entering her body. Her power level broke through ultimate class. And she screamed due to immense pain of raising her power level forcibly.

The two guards escorting Kuroka felts their breath shorten due to the large pressure and backed away from her. The researchers and Nebarius who hadn't gone too far turned around and exclaimed " amazing her power level broke through, this is amazing master if we can study this phenomenon then it will be a great advancement in our project " Nebarius was also fascinated he was only a high High-Class devil has an ultimate class devil as a servant so he also fells giddy but the next scene broke his hopes and turned into anger.

Kuroka who had lost her reasoning was extremely angry ( not berserk ) and directly killed a guard with a chakra enhanced punch through his chest and then twisted her body and burst the head of the other guard with a kick. She then crouched down a little and directly rushed towards the researchers before the others could reach, she covered the distance of 20 metres in a moment and came in front of a guard of Nebarius and used her hand like claws with chakra and slashed the his neck and started massacring everyone until only Nebarius and the head researcher were left.

Nebarius was backing away but he still didn't forget to shout " You bitch what have you done do you know the concequances of this? you'll be hunted by the entire underworld if you don't stop "

Kuroka just looked at him and said " say no more I've had enough of being weak, today if even the Maou came, he wouldn't be able to stop me from killing you " After saying that Kuroka used and claws cut the hands and feet of Nebarius before he could use his magic ( because I don't know what magic he used so I didn't let him use it 8P ) and left him in pain before coming toward head researcher and said " Where is Akira? take me to him ". He could only nod in compliance and went with her.

Before leaving, Kuroka killed her master and went to take Shirone and Silvia with her. She killed all the people that came in her way and successfully took Shirone and Silvia outside and with the head researcher they came in front the door to the room in which Akira was locked in.

" Open the door " ordered Kuroka but the researcher was hesitant and said " thats not a good idea " but under the pressure of Kuroka, he opened it and inside was extremely dim yellow lighting and Akira was chained with spikes embedded into both his palm calf and chest to prevent him from moving.

" BROTHERR "