One new character could be a Diabolos Dragon knight. This character has sworn to protect the Diabolos Dragons at all costs and initially sees Issei as a threat. As the story progresses, they might become friends. A female Diabolos Dragon with the ability to shape - shift into human form could also be introduced. She could be a love interest for Issei or a rival for his affections. And then there's the Diabolos Dragon hatchling that Issei finds and decides to raise, which brings a whole new dynamic to the story.
A new character could be an exiled Diabolos Dragon who has different views from the rest of its kind. It teams up with Issei to change the perception of Diabolos Dragons. There could also be a group of thieves who are after Diabolos Dragon artifacts. Their leader is a cunning and sly character. And a young girl who has a special connection to the Diabolos Dragons' energy source. She might be the key to Issei unlocking a new level of power related to the Diabolos Dragons.
How about a character who is a descendant of an ancient dragon - slaying clan? This character might initially be hostile towards the Vanishing Dragon and its wielder because of their clan's history. But as the story progresses, they could come to understand the difference between the Vanishing Dragon and the ones their clan used to slay, and end up becoming an important ally. They could bring in new fighting techniques and knowledge about dragons.
A young and talented artist could be a new character. The empress could commission the artist to create a portrait or some art for the palace, and in the process, a unique friendship or a complex relationship could develop. The artist could also be a source of inspiration for the empress in different ways.
The allure lies in seeing Issei in a new and powerful form. It's exciting to imagine him as the Diabolos Dragon God and all the possibilities that come with it.
One interesting plot idea could be Issei facing a new and extremely powerful rival in the form of a Diabolos Dragon hybrid. This new foe could have unique powers that Issei has to figure out how to counter. Another idea is Issei having to travel to a different dimension where Diabolos Dragons rule and he has to form alliances to survive. Maybe he discovers a long - lost power within himself that is related to the Diabolos Dragons during his adventures there.
One interesting aspect could be the unique character designs. In many fanfics, the characters are given new traits and backstories that make them stand out. For example, Issei might have different relationships with other characters compared to the original source. Another aspect is the exploration of different storylines. Fanfic writers can take the basic concept of the 'diabolos dragon' and create all kinds of exciting adventures, like battles in new and strange realms.
A skilled samurai girl from the Iron Country. She could be a master of a unique sword - fighting style. Maybe she initially distrusts Naruto because of the differences between ninja and samurai, but later becomes his ally and friend.
A mysterious detective from another city who has a different approach to solving crimes compared to Sherlock. This character could initially be at odds with Molly but later become an ally. Another could be a reclusive scientist who has some dark secrets related to the cases Molly is involved in. There might also be a street - smart informant who has connections in the underworld and provides Molly with valuable information, but at a price.
A new character could be a young hacker who initially starts as an adversary to Terry. This hacker could be trying to expose the secrets of Wayne - Powers but then realizes that there are more dangerous forces at work and ends up teaming with Terry. Another could be a genetically - enhanced enforcer working for a new criminal syndicate in Neo - Gotham. He would have superhuman strength and speed, making him a tough opponent for Terry.
An exiled God. He was banished from his own pantheon for some misdeed. In the Highschool DxD world, he is trying to find a way to redeem himself. He has unique powers that are different from the other characters, and his story could be one of redemption and self - discovery as he interacts with the devils, angels, and fallen angels in the story.
A powerful elder who has been in hiding since the fall of the Land of Whirlpool. He could have a vast knowledge of the land's ancient techniques.