User blog comment:B214/Question and Answers 2/@comment-3965848-20140228143236/@comment-1359322-20140228145235

Actually i don't think Issei will let his parents know that he became a Devil. It's to protect his parents. If Issei's parents learns about the truth, they might indirectly get involved in supernatural incidents that might cause them severe injury or trauma and in the worst case death.