High School DxD Hero: Taiikukan-ura no Holy

Issei Hyoudou and the Gremory household are drawn into a conflict surrounding Asia Argento and the Holy Sword Excalibur, while old tensions among devils, angels, and fallen angels threaten to erupt again. Issei's determination to protect the people close to him places him at the center of a battle where raw power is not enough.

As hidden motives come to light and alliances are tested, Issei must confront an enemy whose strength forces him to reach beyond his limits. The struggle also brings unfinished feelings and loyalties to the surface, setting the Gremory group back on the path their battle was always meant to take.