Meet Akatsuki Kojou – young high schooler who by unexpected turn of events gets turned into the Fourth Progenitor - an immortal being with incredible power. Despite his wish for a normal life that turns out to be impossible. Kojou is regularly dragged into conflict because of his role as a Progenitor, but because of his partner Yukina he always finds a way to cope with them. That is not his only problem though. He has to control his constant blood urges which are provoked by sexual stimulus. All his powers and his twelve familiars are the heritage of the former Fourth Progenitor Avrora Florestine (Kaleid Blood) also known as the strongest Progenitor.