Prologue

Quiet...

...In that dark room, I saw it.

Standing in the open doorway, my body froze as I couldn't take my eyes off the two figures.

Lying on the bed, my friend was breathing heavily, her face was pale as well while her hands were trying to push another girl's body – my own sister, on top of her.

Hirakawa Yui noticed my presence, putting aside her expression that looked like she might collapse at any moment, I could see how her eyes were asking for help.

However, I can't move. Not because I didn't want to, but seeing the wounds on his body, my adrenaline shot up.

This feeling.... Just like that time.

The smell of fresh blood that stabbed my nose, the sweetness that would make any Vampire sink into their passion… Even just by looking at the ecstasy on my sister's face, I could understand how much pleasure she was feeling.

Even though I knew it would be bad if I didn't stop him, but fear got in the way of my intentions. I didn't want to do it, I was afraid, the slightest movement I took, would destroy my concentration on staying sane.

After all, I don't want her to hate me, but, if I don't save her now, I can't stop imagining what will happen to her later, but if I move and lose control like my sister, things– will be very bad.

Huh... What is this... I feel like I'm stuck in an endless loop, thinking about all this makes my head go numb. I wonder, what kind of face am I making now? I was so worried that I might die this way.

What should I do?

"WHAT ARE YOU DOING?!"

—Like a hurricane, hers screams seemed to wake us all up. Running past me, the blonde haired girl threw her shopping bag aside and swiftly approached the two of them. Forcefully separated my sister from Yui, and pushed her away.

"Y-Yui! What the hell happened?! Are you okay?!"

Saikawa Riko. Seeing her who always act cold was in a panic right now, my heart is hurt. As usual, she stole all the words and actions I should have done. But, besides feeling relieved, I also get jealousy and annoyed, really, this makes me the worst.

"Get away...."

My sister who seemed to have come to her senses started to stare at Riko with intense gaze, and slowly, she raised her palms forward.

"Y-you! Do you understand what exactly you've done right now?! Engaging in a contract with her means you've broken the rules–"

Just as Riko was about to finish her sentence, something pushed her flying backwards, sending her back crashing into the wall, before finally falling on the ground.

"Bullshit with that rules."

While casually approaching Yui who was already unconscious, my sister smiled, she's carried Yui body off the bed, and gently caressed the wound on her neck.

And while keeping hers back to me, she looked at me.

"...You're not going to stop me?"

Seeing the expression in his narrowed eyes made it hard for me to guess what he was thinking, I couldn't help but shiver at the back.

Why is all this happening? All these terrible tragedies... Where is the fault?

–Ah, that's right… Come to think of it, it all started from when I introduced my friend Yui, to my sister that day. I never imagined, the look in her eyes that changed when my sister first met with Yui would be the starting point for all of this to happen– No, it's not like that. To be exact, from that day on, something must have happened between the two of them.

Something that, made my sister more than lose control as she is today.