A fight for love ~ Nagisa X Kayano/Karma (COMPLETED)

Nagisa's vision

Around the same time as Kayano dreamt of Nami, Nagisa had collapsed on his couch after a hard day of teaching, and seen...  Something.  Or someone.  A girl, with hair of purple, and eyes of red.  She was looking at him.  "Hi!" She giggled, "Long time no see!"
"I'm sorry, who are you?" Nagisa asked, confused.
"You don't need to know that!  All you need to know, is that I'm here to help you!" ,
"In what?"
"The problem, of course!  I'm talking about Karma, silly!  And some others too..."
"How will you help?"
"Well, I'll just give you some advice: Kill him."
"I can't do that!"
"Oh but you can!" She grinned, as if this wasn't insane, "You're stronger than him.  You could easily-"
"Korosensei taught me not to kill anyone!"
"Korosensei doesn't know what you've been through, he doesn't know you.  But I do.  I know who you are.  I care about what happens to you.  Your 'friends' don't care.  Korosensei doesn't care."
"Of course he does!"
"He's using you."
"Y-you're Lying!"
The girl smiled, and stood up to face Nagisa.  "Fine.  See what happens when you say no." She flicked her wrist, and Nagisa doubled over, screaming over and over in pain.  Crying for someone, anyone to end it already!  "Help me!  Mum!  Dad!  Kayano!  Help me!  Please!" Over and over again, he called out in the desperate yet futile hope that someone could hear. 
The girl smiled once more.
"Why are you crying?" She mocked, "Nothing's wrong.  So why are you upset?"
"P-please, stop..." Nagisa begged, "I can't take it... Much longer..." He was coughing blood now, he looked like he was about to die.  The girl stopped, and looked at him with an almost amused expression.  "Hear me out then!  If you kill them, everything will be okay!  All your problems will be solved!  I won't force you to do anything, but think about it." Nagisa was suddenly flooded by his own memories.

He saw himself on the edge of sanity, about to kill Takaoka, Terasaka trying to stop him, but this time... He couldn't hear the warnings of the group, and was flooded by bloodlust and desire to hurt.  To kill.  He smiled, as he chose the knife, and walked to Takaoka with it, not even smiling.  He was confused.  He quickly sliced Takaoka's neck, and he fell to the ground, dead.  His group were distraught, but he didn't care.  All his problems were over.  Vengeance could help him.  Killing was the only way...

"No!" Nagisa shouted, quickly jolting himself back to reality, "Killing will never be right!"
"Those are your own thoughts, Nagisa, your own emotions.  You were in control.  You chose to kill."
"But that's not real!"
"It's as real as this reality.  But in a world where you chose to go with your own instincts, and not to be controlled by idiots like them."
Nagisa went silent. 
"Well, just something to think about," she grinned, "see ya, Dad."

Nagisa tried to call out a name, just a name he had in his head, but no sound came out of his mouth.  Somehow he knew that the name was the girl's, but he couldn't say it.  He couldn't call her.  So he settled for this:

"What have you become, Kumori?"