It could be Issei. Since he's always eager to become stronger and protect his friends, his encounter with the Annihilation Maker could lead to some really interesting storylines. He might be drawn to the Annihilation Maker's power and seek to learn from them to gain an edge in battles against the various threats in the High School DxD world.
A plot could involve the Annihilation Maker creating a device that can enhance or steal the powers of the characters in High School DxD. This device falls into the wrong hands, like a group of rogue exorcists who want to use it to purify all the devils and fallen angels. The main characters then have to race against time to retrieve the device from the exorcists. Along the way, they face many challenges and battles, and the Annihilation Maker has to use their skills to reverse the effects of the device if it has already been used on some of the characters.
I'm not entirely sure as it depends on the specific fanfic. But typically, you might expect to see Issei Hyoudou as a main character, since he's central in the original High School DxD series. He might have different developments or face new challenges in this fanfic.
A psyker might be the main character. Given their connection to the warp, they could sense the power of the Annihilation Maker from afar. They might be drawn to it, either out of curiosity or because they believe they can control it. But they soon find themselves in over their head as the power of the Annihilation Maker is far greater than they expected.
I'm not entirely sure specifically as it could be a very niche or even a made - up concept within a particular fan community. It might involve some sort of story in the 'High School DxD' universe where there's a concept of 'annihilation' and a'maker' which could be a character or a force that causes annihilation. But without more context, it's hard to say for sure.
A human with a special power that makes them a killer could also be a good choice. They could be an outcast in the human world because of their power, and then get drawn into the High School DxD world. Their journey from being a feared killer to finding a place among the supernatural beings would be an exciting story to tell.
It's hard to say without reading it, but it could be Harry Potter himself. He might be trying to stop the annihilation maker from causing destruction. Or it could be a new character created by the fanfic author who has a special connection to the annihilation maker.
I'm sorry, I don't have specific recommendations for 'dxd annihilation maker fanfiction' as it's a very specific sub - genre. You could try searching on popular fanfiction websites like Archive of Our Own or FanFiction.net and use those keywords to find relevant stories.
The power dynamics can also be really engaging. Maybe in 'annihilation maker dxd fanfic', the way powers are used and developed is different. Some characters could gain new abilities or find different ways to utilize their existing ones. This can lead to intense battles and strategic planning within the story.
Rias could also be the main character in such a story. Imagine if she goes through some sort of magical accident that makes her gain weight. As a high - status devil, this would be a huge blow to her self - image. She might become a slob as she struggles to come to terms with her new body, and it could be interesting to see how she tries to regain her confidence and status within the school and the devil society.
It could be a powerful devil who sees the Ghost Rider as a threat to his plans in the school. Maybe this devil wants to take over the school or gain more power among the students, and the Ghost Rider's presence and his sense of justice stand in the way.