Sayaka Kirasaka is a member of the Lion King Organization, which is assigned to the Multinational Magical Crimes under the Foreign Affairs Division. She is Dmitri Vatler's observer and is a "War Dancer" who specializes in using hexes and assassinations.

Kirasaka and Himeragi are very close and were former roommates during their training in the organization. Her unusual protective behavior for Himeragi may suggest that she has some sort of feelings for her. She also despises Kojou so much that she plans to eliminate him. 

She uses a sword called "Koukarin" that can nullify any physical attacks. It can also change into a bow called "Der Freischütz" which she uses to shoot magical arrows and spread any incantations over a wide area.


The Fourth Primogenitor—That's the world's strongest vampire that should only exist in legends. Accompanied by twelve Kenjuu and spreading calamity, this phantom vampire appeared in Japan. For the observation and obliteration of this Fourth Primogenitor, the government and Lion King decided to dispatch an attack mage known as a Sword Shaman. However, for some reason, the one chosen for the observation was a apprentice Sword Shaman girl, Himegari Yukina. Wielding the strongest anti-primogenitor spirit spear, Yukina arrived at Demon District, Itogami City. What is the true identity of the Fourth Primogenitor, Akatsuki Kojou, she encountered over there!? 
(Source: Baka-Tsuki, edited)

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The second season of Strike the Blood. The adaptation of 9th, 11th and 12th LN volumes.

The third season of Strike the Blood. 
 
It was announced at a Dengeki Game Festival stage event that the Strike the Blood light novel series will get a third OVA release. It will cover until the end of Seisen-hen. 
 
(Source: MAL news)

The fourth season of Strike the Blood.

The fifth season of Strike the Blood.

Kojou and Yukina are on their way to school as usual when they find La Folia being chased by someone. Yukina crosses blades with the enormous man who's pursuing her, but before the fight can escalate further, La Folia makes a shocking comment: "Father, this is the Fourth Progenitor, Akatsuki Kojou... my first!" La Folia's father, Lucas, had told her to decide who she wished to marry, so she declares that Kojou is her choice. Lucas refuses to accept this, but then La Folia's mother, Polifonia, invites Kojou and Yukina to a party so they can all talk in more detail. When they arrive at the party, they discover that Asagi, Yaze, Nagisa, and Sayaka have been invited as well, due to their connections with Kojou. What sort of heated battle is about to break out between the many girls in Kojou's life?! 
 
(Source: Crunchyroll)

While several of the girls investigate Vatlers ship afloat, Akatsuki and Himeragi wake up alone in the school gym with no memories of the day before and no explanation for why they were asleep on the same futon and why Himeragi is wearing an old-fashioned school PE uniform with bloomers. A bloody baseball bat and missing weapon soon deepen the mystery as assorted forces race to solve the mystery of the empty boat, the bloody bat, and the purple bra in the MCs pockets!

He never asked for this power.
 
Kojou Akatsuki used to be an ordinary high school boy--but that was before he became the Fourth Primogenitor, the most powerful vampire of all time. Worse--he doesn't even remember how it happened. Middle schooler Yukina Himeragi, meanwhile, is the Attack Mage sent to observe him--and to stop him if he gets out of control. But was it really a good idea to send a cute girl to observe a massively powerful vampire boy whose abilities activate whenever he gets aroused? And on an artificial island populated with all manner of demonic individuals, each with their own designs on the Fourth Primogenitor--?!
 
(Source: Yen Press)