Strike the Blood, Vol. 16 (light novel): The Mirage Paladin

On the brink of death, a young man washes up on a mysterious shore. He is found by a sword-wielding woman named Shizuri Kasugaya, who informs him that he is Kojou Akatsuki, the Fourth Primogenitor and the World's Mightiest Vampire! Having lost most of his vampiric abilities, he begins training as an Attack Mage with Shizuri. And in the days spent healing his mind and body, the pair encounter someone new: a beautiful specter wielding a silver spear who calls Kojou "Senpai."