Perhaps they are hiding because they have stumbled upon a secret that many powerful beings in both universes don't want them to know. While under Rias, they start to figure out the mystery. Kiba might use his knowledge of chakra and ninja techniques to keep their hiding place concealed, and Issei could use his connection with the devils to gather some inside information. Along the way, they might make new friends or enemies from both Naruto and High School DxD worlds.
Their relationships could develop in a very interesting way. Kiba, being a ninja, might be initially suspicious of Issei's more brash and perverted ways. However, as they are in this situation together under Rias, they start to understand each other better. Issei might learn some discipline from Kiba, and Kiba could become more open - minded because of Issei.
There could be a storyline where Naruto is summoned to the High School DxD world by some ancient magic. He is seen as a powerful ally or a threat depending on who you ask. Rias takes it upon herself to figure out Naruto's intentions. As she gets to know him, she realizes that his values of friendship and protecting the weak are similar to her own. Together, they start a journey to stop a dark force that is rising in the DxD world, with Naruto teaching the devils some ninja techniques along the way.
In this type of fanfiction, the author might be trying to create a new narrative by bashing Kiba. It could be that they have a particular vision for how the Naruto and High School DxD worlds blend together. Maybe they think Kiba's character doesn't fit well in their idea of the crossover, so they use him as a sort of 'villain' or an obstacle for the other characters to overcome. This can add drama and a new layer of storytelling to the fan - made universe.
Kiba has his Inuzuka clan abilities. His connection with his dog, Akamaru, could be very useful. For example, Akamaru could be on the lookout while they are hiding, sensing any approaching danger long before they do. Issei, on the other hand, if we consider his abilities from High School DxD, he has his boosted gear which gives him power. He could potentially use it to defend their hiding place if they are discovered.
One possible reason for such a fanfiction could be to explore a different dynamic in the story. Maybe the author wants to show a more complex relationship where Issei has some deep - seated issues with Rias' leadership style or her decisions. It could also be a way to create conflict and drama, which are essential elements in fan - created stories.
One possible idea for this fanfiction could be Naruto being transported to the world of High School DxD. He might end up attending the same school as Rias. Given Naruto's strong sense of justice and his combat skills, he could quickly become involved in the supernatural battles and power struggles in that world. He might also form an interesting relationship with Rias, perhaps starting as friends and gradually developing into something more as they face various challenges together.
One possible fanfiction could be about Naruto characters attending the school in High School DxD. For example, Naruto's positive and determined attitude might clash with the more complex social and power dynamics in the DxD world. He could make new friends or even rivals among the devils, angels, and fallen angels.
One possible fanfiction could be about Naruto characters somehow ending up in the world of High School DxD. Maybe Naruto's skills in combat and his determination would make him a formidable opponent in the battles that often occur in the High School DxD universe. He could form interesting alliances or rivalries with the characters there.
A fanfiction might explore how the power of the Excalibur in High School DxD would interact with Naruto's chakra. Since the Excalibur is a powerful holy weapon, it could have some interesting reactions when in the presence of Naruto's unique chakra, which is different from the magic in the High School DxD world. For example, it could either enhance or nullify certain abilities depending on how the author writes it.
In a Naruto - High School DxD fanfiction, the power levels would be really interesting to explore. Naruto's sage mode and tailed - beast forms are extremely powerful. In the DxD world, there are different power systems like the Sacred Gears. It would be fascinating to see how Naruto's powers interact with the powers of the DxD characters. For example, could his Rasengan be enhanced by a Sacred Gear? Or how would he fare against a devil's magic?