Meiga Itogami

He is a prisoner who managed to escape with six others including Aya Tokoyogi when the Prison barrier's seal was broken. All the prisoners then agreed to help Aya to look for Natsuki Minamiya and then kill her so that they'll be completely free. However, he was the only other criminal that was smart enough to not search for her because he had deducted that since Aya Tokoyogi got all of Natsuki Minamiya's memories and time, then it meant that she is now the key of the prison barrier and claimed that all the other prisoners are now searching for no reason. Furthermore, he went on and said that he'll not spoil her plan because it will also benefit him. He also noticed that Asagi could be the priestess of Cain.

First appearance
Anime Debut: Episode 16 (Fiesta for the observers I)

(Source: Strike the Blood Wikia)