On the wraparound jacket band on Gakuto Mikumo’s 15th Strike the Blood light novel volume, it was announced that a new OVA series has been green-lit, an image showing the announcement will be shown later in the article. There will be more details announced for the OVA at a later date, let it also be known that the jacket band notes that the novel series is in the final part of the Seisen arc. The series began as a light novel that started May 10th 2011 and is still ongoing, its later manga adaption started June 27th 2012 and is continuing publication as well. Mind you that the series would later get a 24 episode anime adaption starting on October 4th 2013 and end March 28th 2014 and also receive an OVA. Yen press is currently publishing the light novel series in North America and published the second volume on January 19th and will publish the third volume May 24th.
Finally below is a plot summary of the series quoted from MAL:
The Fourth Progenitor is a name that strikes fear in many people. A dangerous vampire thought to exist only in legend, the Fourth Progenitor commands so much power that its very existence is considered an act of war. But now people have discovered that not only is the Fourth Progenitor very real, he is also currently living in Itogami City, an island where humans and demons live together freely.Until three months ago, Kojou Akatsuki was a normal, human high school student. After becoming the Fourth Progenitor, though, he finds himself with abilities far beyond those of regular vampires. One day, he meets Yukina Himeragi, an apprentice sword-shaman who is sent to observe him and kill him if he becomes too much of a threat. However, her presence raises many questions. If the Fourth Progenitor is so dangerous, why send only an apprentice to deal with him? And how did a human become the Fourth Progenitor in the first place?