Many fanfictions show Vergil as a bit of an enigma in the School DxD world. His past from DMC, his quest for power, and his family history all add depth to his character in this new setting. His relationship with Akeno can be seen as a way to explore his more emotional side. For instance, Akeno might be the one to break through his cold exterior and make him more involved in the community of the school, while at the same time, Vergil's presence affects the power dynamics and the overall story arc in the School DxD fanfiction world.
The characters in DxD would be quite shocked at first. Ichigo's appearance and his powers are so different from what they are used to. For example, Rias Gremory would probably be intrigued by Ichigo. She might try to form an alliance with him, seeing his potential as a powerful ally. Issei, being the main character in DxD, would likely be both jealous and in awe of Ichigo's abilities, and might challenge him at first but then learn from him over time.
One common character paired with Vergil is Dante. Some fanfictions explore a romantic relationship between them, which often delves into the complex dynamic of their brotherly bond and how it could transform into something more. It's a very unique take on their relationship.
Nero is also a popular character to be paired with the reborn as Vergil. Given Nero's connection to Vergil in the original story, in fanfiction, their interactions can range from mentorship - where Vergil helps Nero master his powers, to more adversarial relationships if the reborn Vergil has different motives.
Issei would probably be the first to want to fight Thanos. He's always eager to prove himself and protect his friends. He might initially underestimate Thanos due to his own growing power and confidence, but soon realize how powerful Thanos really is. Rias would be more cautious. She would likely try to gather information about Thanos first and then formulate a plan to either fight or negotiate with him.
Issei, being the hot - blooded character he is, would probably be excited to meet someone as powerful as Naruto. He might challenge Naruto to a friendly spar at first, hoping to learn from him and test his own strength. And as he gets to know Naruto better, he could start to see him as a brother - in - arms, especially if they face common enemies together.
Rias would be devastated. Issei was not only her servant but also someone she had deep feelings for. She would likely go into a rage at first, vowing to find and punish whoever was responsible. Akeno would be heartbroken as well. She and Issei had a special bond, and she would be in mourning for a long time. Kiba might feel a sense of guilt, wondering if he could have done more to protect Issei. Asia would be in shock and constantly pray for Issei's soul, hoping for some kind of miracle.
Issei would probably be both scared and excited. He's used to dealing with powerful beings, but the Ghost Rider is on a whole different level. He might initially try to fight him out of bravado, but soon realize he's outmatched. Rias would be more cautious. She would see the Ghost Rider as a potential threat to her peerage and would try to figure out his motives before taking any action.
In fanfiction, female Vergil often has different emotional expressions. While the original Vergil is stoic and reserved, female Vergil might be more in touch with her emotions. For example, she could show more vulnerability when dealing with the loss of her family. Also, her fighting style might be more fluid and graceful compared to the original Vergil's more brute - force - like approach.
Often, Vergil will start by observing Nero in battle. He's curious about Nero's skills and the source of his power. So, he'll watch from the shadows, analyzing Nero's every move.