User blog comment:B214/Question and Answers 6/@comment-50.139.232.230-20161016013521/@comment-10330822-20161021113500

Penetrate makes his offense better because it goes through defense. So it can change his fighting style depending on the enemy. Issei is kind of just becoming more and more of a power maniac, a true juggernaut. Between the CCP, his Wyverns, Longinus Smasher, and DxD, he can plow through almost anything. Really, he's very similar to most shonen characters, the fighting style isn't changing, he's just getting more and more powerful.