I, the Holy Son, Azathoth

After escaping from the site of a cult ritual, I headed to the Academy, which was surrounded by a barrier, to figure out what had happened to me. But I never expected to face an unimaginable ordeal: a peaceful school had become a paradise for lurking monsters, and the barrier of Azathoth had trapped us inside like a cage. To save my own life, I took action... (from Chapter Three)

Chapter One: Emiya Shirou, Horikita Suzune, Saya

Chapters Two–Three: Kotomine Kirei, Horikita Suzune, Karuizawa Kei, Ichinose Honami