High School DxD Vol. 12 (Light Novel)

In Vol. 12, with the loss of Issei, the Gremory family is in disarray. As everyone battles with their grief, the Hero Faction uses the opportunity to make their move. Worse still, the Underworld is in danger when gigantic monsters suddenly appear and begin marching toward the cities. What will the Gremory family do? And what about Issei?
Notice: This book is written in Japanese.