Detective Sebastian Costa is a morally-driven human cop with a personality similar to Cameron, determined to do good. At first skeptical about the existence of the Vampire Guardian Angels, he was in the beginning suspicious of Ms. Price, but soon found out they were real and, as he fought to save her from them, he and Ms. Price grew close.
Costa is a brave detective, but he is easily frustrated and impatient, temperamental, and cocky, and at times unsure of how to handle himself in situations involving the Vampire Guardian Angels so he always tends to look to Cameron for guidance and even help. But he cares about doing the right thing as much as Cameron does and wants to protect humans, especially the Author, Ms. Price, who he was dating. He fights to retain his own humanity in a world taken over by Vampire Guardian Angels and finds himself often overwhelmed.
He becomes even more determined when Ms. Price is kidnapped by Jeromos, and he fears the worst for her, which drives him to do anything and everything to find her. He wants to become a better fighter and knows that Cameron may not always be there, and puts pressure on himself to take the initiative and control of situations.