If Naruto reincarnates as Issei, the plot could be really exciting. Naruto's reincarnation would bring his own set of values and skills. He would first have to deal with the fact that he's in a different body and a different world with different rules. He might initially struggle with the perverted nature of Issei's character, but gradually change it to be more in line with his own values. In battles, he would use his Naruto - like combat abilities, such as shadow clones and rasengan. He could also use his experience in making friends and allies in Konoha to form stronger relationships in the High School DxD world. This could lead to new alliances between devils, angels, and other factions, completely changing the way the story unfolds.
The plot might start with Naruto being confused about his new identity as Issei. But soon, he'd start to use his chakra and ninjutsu to gain an edge. He could also change the relationships Issei has. For instance, he might approach the devils with more caution and suspicion due to his ninja upbringing. As the story progresses, he could introduce new combat styles and strategies, shaking up the power balance in the world of High School DxD. And he might also try to find a way to bring some of the values he held dear in the Naruto world, like loyalty and perseverance, to this new world.
The plot could involve Naruto having to adapt to Issei's world of devils, angels, and fallen angels. He'd likely use his ninja skills to stand out. Maybe he'd try to form a different kind of peerage, using his knowledge of teamwork from Konoha.