High School DxD Novel Volume 12 was written by Ichiei Ishibumi and features illustrations by Miyama-Zero.

A swarm of giant monsters has appeared and threatens to destroy the underworld, yet Issei...is nowhere to be found. He’s gone, and the rest of the Gremory Familia is in pieces without him. I, Yuuto Kiba, can only push forward in the face of death. Issei, please lend me just a little bit of your courage. I’m going to need it.