Accel World, Vol. 8 (light novel): The Binary Stars of Destiny — Reki Kawahara

Haruyuki's desperate battle with his friend Takumu has taken him to the brink, and he finally activates the Destiny, a purified version of the notorious Armor of Catastrophe. It's light versus dark as their fierce fight continues, and the stakes couldn't be higher. If Haruyuki can't rid his friend of the sinister ISS kit that's infected him, Takumu could be lost to the darkness forever. And he just might take Haruyuki with him...