Fiesta for the Observers (観測者たちの宴 Kansoku sha tachi no utage) is the fifth novel of the Strike the Blood series.
Aya Tokoyogi and six other hardened magical criminals have broken out from imprisonment. Their goal—to completely erase the 'Witch of the Void,' Natsuki Minamiya, from existence. How these events will unfold in the Demon District will depend on the actions of the strongest vampire to ever exist, Kojou Akatsuki.
- Chapter One: Absence of the Witch
- Chapter Two: The Pursued vs. the Jail Breakers
- Chapter Three: The Oceanus Grave II
- Chapter Four: Erosion of Darkness
- Chapter Five: Fiesta for the Observers
The volume was adapted into episodes 16-19 of the anime.