Great chapter author-san. Just a correction: The POD (Power of Destruction) comes from the Bael, that is, from Rias's mother, Venelana. In the series it was never said, but in the Ars Goetia, the Gremory had the power to enchant both young and old, and the power to see the future for a few seconds.
Will Aika join his harem.? later.? It is obvius Katase and Murayama like him then a friend. They just need to fix things between each other Because of what happened in the past. So Aika and Issei should also get closer.
