The characters from Naruto can be integrated by having their powers be seen as a new type of power in the DxD world. For example, Naruto's Rasengan could be considered a powerful attack similar to a Sacred Gear's special ability. Sasuke's Sharingan could be something that the devils or other DxD characters are intrigued by and might try to either copy or study.
Naruto would probably be very friendly and curious. He'd be excited to meet all the different types of beings in the Highschool DxD world. He might start by trying to make friends with Issei, sharing his stories about his own battles and adventures in his world.
One possible scenario in such a fanfic could be that Naruto is betrayed by his new comrades in the DxD world. Maybe they misunderstand his motives or are jealous of his power. For example, they might think he's using his abilities for his own gain rather than the common good.
I'm not sure if there is a specific fanfic exactly like that. There are a vast number of fanfics out there, and it might be a rather unique or niche combination. You could try searching on some major fanfic platforms like FanFiction.net or Archive of Our Own to see if such a story exists.
He could be a new type of threat or ally in the DxD world. Since Naruto has such powerful abilities, the fallen angels might see him as a potential weapon or a hindrance to their plans.
One possible plot could be Naruto being summoned into the DxD world by some sort of magic accident. He might initially be confused but quickly adapt his ninja skills to the new environment. He could team up with some of the DxD characters to face a common enemy, like a powerful fallen angel or a rogue devil. His Rasengan and shadow clone techniques would be quite unique in this world.
The contrast. When a fanfic features a weak character in the Naruto DxD universe, it creates an interesting dynamic. For example, seeing a character with less power try to survive in a world full of powerful ninjas and devils makes for an exciting read as they have to rely on their wits more than their strength.
In 'naruto angel dxd fanfic', the characters from both Naruto and DxD get to interact in ways that are not possible in their original stories. For example, Naruto's sense of justice and his never - give - up attitude can have a big impact on the DxD characters. Also, the different power systems collide and sometimes merge, like Naruto's chakra with the magic in DxD. This can lead to really unique and unexpected plot twists. It's not just about putting the characters together, but also about how their worlds' concepts interact.
One popular 'Naruto Otsutsuki DxD Fanfic' is 'Naruto: Shinobi of the Underworld'. It combines the elements of the Naruto universe with the unique aspects of High School DxD in an interesting way. The story often has Naruto facing new challenges and using his shinobi skills in a different, more supernatural setting.
Power is a major theme. The Kyuubi gives Naruto immense power, and in the DxD world which is also full of powerful beings, the exploration of how this power is used and controlled is often central.