Strike the Blood, Vol. 2 (manga)

Yukina is trapped in a pitched battle against Astarte the homunculus, and she's losing--when who should come to her rescue but the very boy she's been assigned to observe, Kojo Akatsuki! Akatsuki tries to end the clash, but Astarte's familiar, the fearsome Rhododactylos, isn't going to let that happen. Is this a fight that only an awakened Fourth Primogenitor can finish?