There's a fanfiction where Issei's son has a unique power that sets him apart. In this story, he has to learn to control it while also handling the typical Highschool DxD drama like rivalries and romances. The author does a great job of showing how he struggles with being in his father's shadow at times, but also rises above it in his own way.
I haven't read this particular fanfiction yet, but generally, a fanfiction about the son of Sirzechs in the Highschool DxD universe could be really interesting. It might explore new powers, relationships, and storylines that the original series didn't cover. For example, how the OC would interact with the existing characters like Issei and Rias, and how his heritage as the son of Sirzechs would shape his destiny in the Devil society.
The OC, as the Son of Sparda, could fit in by being a new and powerful entity. He might be initially seen as an outsider, but his powers would quickly draw attention. He could become involved in the power struggles between the different factions in Highschool DxD. For example, the devils might try to recruit him, while the angels might be wary of his presence. His unique abilities would also make him a valuable ally or a fearsome opponent. And in the high school setting, he could be a bit of an enigma to the other students, both human and supernatural.
Romance is also a big theme. Just like in the original Highschool DxD, his son usually has his own love interests. These relationships can be complicated by his status as Issei's son. Sometimes, potential partners are attracted to him because of his family name, and he has to figure out if their feelings are genuine.
Well, in this fanfiction, Naruto's origin as the son of Amaterasu could lead to a story where he is initially shunned by some in the DxD world because of his strange powers. But as he proves himself in battles and shows his kind heart, he starts to gain allies. His journey could also be about uncovering the secrets of his mother Amaterasu and how that relates to the overall balance of power in the DxD universe. Maybe he has to face an ancient evil that only his combined ninja and divine powers can defeat.
The plot could involve Naruto being an outcast in the DxD world at first because of his strange origin as the son of Shiva. But then, as he shows his strength and determination, he gradually earns the respect of the various factions. He could introduce some ninja concepts like shadow clones to the DxD characters, which they could use in their battles. And his connection to Shiva might give him some divine powers that are both a boon and a burden as he tries to find his place in this new world.
I'm not sure who the author of this particular fanfiction is. There are so many fanfiction writers out there, and it can be hard to track down the originator of a specific one like this.
Well, without reading it specifically, it could be about a very unique alternate universe where Harry Potter is the son of Gabriel in the DxD (High School DxD) universe. Maybe it combines the magic from the Harry Potter world with the supernatural elements of DxD, like devils, angels and fallen angels.
Obviously, the son of Trihexa is one of the main characters. His actions and development would be central to the story. Then there could be characters from the original 'Highschool DxD' series like Issei, who might interact with this new character in various ways, either as an ally or an opponent. Rias could also be a main character as she is an important figure in the original series and her reaction to the son of Trihexa would be significant.
It's also unique in terms of character interactions. Naruto's values from his ninja world clash and blend with the values of the DxD characters. For example, his sense of loyalty and friendship is put to the test in a world where power struggles between different factions are common. And his Sparda - like powers make him a target and a potential ally to many in the DxD world.