User blog comment:B214/Question & Answers 5/@comment-77.97.12.117-20150705214444/@comment-26108673-20150706014415

I agree with Maze. He has quite the knowledge about the Underwold. Simply knowing all 72 Pillars in order is an amazing feat, at least for me. XD Like Maze also said, Issei had classes with a personal teacher assigned by Venelana about manners and underworld history. If I'm not mistaken, he only had trouble with underworld's culture and traditions. Well, considering that he was originally human, that is to be expected. He also learned about mythological creatures and met several of them. It's very rare to see him saying: I never heard about that creature or this person. In my opinion, he has no problem in knowledge about underworld, he only needs way more experience.