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.
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.
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.
The story could develop with Issei forming his own group. He might gather other characters who also feel left out or have similar goals. This new group could then become a rival to Rias' peerage, leading to interesting battles and power plays.
At first, the relationship might become strained. Kiba and Issei might be a bit wary of Naruto because of whatever is making them twitchy. However, as the story progresses, they could start to communicate more. Naruto might realize that his actions are causing them discomfort and try to make amends. This could lead to a deeper understanding among them.
Some people might write such bashing fanfiction because they prefer other characters or storylines over Naruto, Rias, and Issei. Maybe they want to create a different narrative where these characters don't overshadow their favorites. It could also be a form of creative expression to explore how a story would be different without them.
Well, one possibility could be that they are hiding from some sort of danger. Maybe there's a powerful enemy in the Naruto world and in the Issei's world (assuming it's from High School DxD) that they need to avoid. And Risa's place is the only safe haven for the moment. They might be waiting for an opportunity to strike back or for help to arrive.
Some fanfictions explore a romantic relationship between Naruto and Sakura, with Sasuke being the supportive friend. Naruto and Sakura start to notice the little things about each other. Naruto is always there to cheer Sakura up when she has a bad day at the hospital, and Sakura helps Naruto with his Hokage duties. Sasuke, with his own experiences, gives them advice on how to make their relationship work.
At first, Rias' brother would see Naruto as a threat to his relationship with his sister. But as time goes on, if Naruto shows that he has no romantic intentions towards Rias and is just a friend, the brother might start to warm up to him. Rias would appreciate Naruto for being able to handle her brother's brocon behavior better than others. And Naruto would just be his usual friendly self, gradually becoming part of their little group.
Well, it could start with Naruto being a bit clueless about fatherhood at first. He might try to teach Issei some of his ninja skills, like how to throw a kunai or use chakra. As time goes on, they could bond over protecting their home from threats. Naruto's never - give - up attitude would also influence Issei, making him more determined in his own pursuits.
Some villagers might start to miss them. Naruto has always been a source of inspiration for many in the village, and Kiba is also well - known. Their departure could make some realize how important they were. Others might feel betrayed, thinking that they are deserting the village in a time of need.