It replayed in Hibiki’s head once she figured out who killed her twin sister Kanade it was her friend Setsuka who did it.

“I killed her..”

Setsuka admitted as she stands across from Hibiki, her mind racing as her friend got rid of the thing she held dearest her younger twin sister Kanade was gone, Hibiki couldn’t live with it at all, being in a killing game made Hibiki sick but without Kanade it was worse.