His relationship with Rias would likely become more complex. She might see him in a new light, both as a powerful being in his own right and also as someone with a great destiny. There could be some tension as she tries to figure out how to interact with him now.
Perhaps Issei discovers that his connection to Great Red gives him the ability to travel to different realms more easily. This could lead to him exploring new places, making new allies and enemies, and learning more about his true nature. It could also involve him having to protect these realms from threats that only he, as the son of Great Red, can face.
In a fanfiction where Issei turns into a dragon, his relationships would be in flux. His relationship with his mentors or those he looks up to might change as they now see him as a different kind of being. They might treat him with more caution or more respect depending on how they view dragons. His friendships with his peers would also be altered. Some might see him as a weapon to be used in their battles or struggles, while others would see him as a friend in need of support. Romantically, if he had feelings for someone, that person would have to deal with the fact that Issei is no longer fully human. There could be jealousy from others who might want to be with the powerful dragon - Issei, or there could be newfound admiration from those who previously overlooked him.
With his female friends, there could be a shift in the dynamic as well. They might be more open with him now that he's a girl, sharing secrets and experiences that they previously wouldn't have. He could also become more involved in 'girl - only' activities, strengthening those friendships in new ways.
Well, if Superman were in High School DxD fanfiction, the power dynamics would be completely shifted. Superman's super strength, flight, and heat vision would make him a dominant force. He might be seen as a rival to the devils and angels in the DxD universe. His moral code would also likely influence the more hedonistic characters in the series.
The friends' reactions would depend on their own personalities and relationships with Issei and Rias. For instance, Rossweisse, being a Valkyrie, might have a more cautious approach. She could be worried about the potential disruption to the balance between the different supernatural groups. Meanwhile, Irina, with her strong beliefs, might struggle initially to accept the situation but eventually come around due to her friendship with Issei and Rias. And of course, all of their friends would likely rally around them to help with the challenges that come with a pregnancy in the High School DxD world.
His relationship with his ninja friends would likely be strained at first. They might be confused or even a bit scared of his new powers. For example, Sasuke might see him as a greater threat now. But Naruto would try to convince them that he's still the same person. With his new divine family, he might have a rocky start too. Zeus could be a demanding father figure, and Naruto would have to stand up to him to protect his ninja way of life.
Well, Issei in High School DxD fanfiction is significant for multiple reasons. He is the protagonist in the original series, so in fanfiction, he serves as the anchor for many alternate storylines. Writers can explore his backstory more deeply, like his family life before becoming a devil. His interactions with different factions in the High School DxD universe, such as the devils, angels, and fallen angels, offer a wealth of possibilities for fanfiction. Fanfiction can also focus on his training and how he hones his skills, which is an exciting aspect for many fans.
Well, he may initially feel a great sense of loneliness. However, Issei is a resilient character. He could use the memory of his parents as motivation. For example, if his parents always wanted him to be strong, he might strive to become stronger in the supernatural world he's now part of. He may also look for answers about their deaths, which could lead him on various adventures in the fanfiction.
Well, if Naruto Juubi was in High School DxD fanfiction, the storyline would change drastically. For one, the power dynamics would be completely different. Naruto Juubi is extremely powerful, and in the High School DxD world which already has a complex power system, it would disrupt the existing balance. The characters in High School DxD would have to adapt to this new, overpowering force. Maybe some would try to ally with it, while others would see it as a threat. Also, the cultural and personality differences between the Naruto universe and High School DxD would create interesting interactions. Naruto Juubi's values from the Naruto world might clash or blend with the more modern and somewhat hedonistic values of the High School DxD characters.
Well, if Naruto's Hiraishin was introduced into the High School DxD universe, it would likely create a huge shift. Characters in DxD would be astounded by the sudden appearance of this teleportation jutsu. It could change battle dynamics completely. For example, in a fight against a powerful devil, Naruto could use Hiraishin to quickly close the gap and land a surprise attack. It might also lead to new alliances as characters try to understand and utilize this new power.