Summer Break! Off to the Underworld!.Issei has recurring visions of Raynare that cause him to question the girls around him. After another hectic morning with Rias, Akeno and Asia, Issei discovers that the Hyodo residence has been rebuilt as a six-story mansion including a training ground, bath and swimming pool. His parents are easily deceived, thinking that the Gremory family works in the construction business. Summer vacation is coming up, and the Occult Research Club members are going on a trip to the underworld. They enter by means of a protected train route, encountering Sona, Genshiro and Tsubaki also on their way to the underworld. Koneko is quiet and subdued during their trip. A surprise attack planned by Azazel helps determine what sort of training each member needs. While at the hot springs, Azazel expands Issei's perverted knowledge of the female body. Elsewhere, a nekomata named Kuroka intends to meet Koneko, her little sister.