User blog comment:B214/High School DxD EX/@comment-4547267-20150903154600/@comment-4547267-20150903225702

Yup, and not only that, Issei is married to Rias, the head of her clan, meaning he have duty to perform, whether he is a true Gremory or not, because whatever he do, will affect the clan images and Rias. Since Issei doesn't want to disapoint Rias or make his kids think he is a lazy no good slacker, he have to work. It's better for the kids to think your busy than a slacker.