High School DxD, Vol. 4 (light novel)

Guess what? I, Issei Hyoudou, am now a mentor to a new junior in the Occult Research Club! Yeah! Demon Lord Sirzechs had the Prez add a Bishop to her Familia. Wait...Hes a what? He was sealed where? Huh? The Demons, Angels, and Fallen Angels are h...