He might also interact with Rias. Rias is a powerful devil and a leader. Sans could approach her with his laid - back attitude. She might be initially suspicious of him but later come to respect his abilities. They could have some strategic discussions about dealing with common enemies in the High School DxD world. And Sans could probably crack some jokes that would either amuse or baffle Rias.
One possible plot could be Sans getting involved in the supernatural battles in the High School DxD universe. Maybe he uses his unique abilities from his original game to help out the main characters in a fight against a powerful enemy. For example, his bone attacks could be a useful addition to the combat arsenal in that world.
One common theme is power dynamics. Since 'godlike sans' is, well, godlike, it often changes the power balance in the 'High School DxD' world. Another theme could be the clash of cultures, as 'sans' comes from a very different universe compared to the one in 'High School DxD'.
Yes, there are some. You can start by looking on fanfiction platforms like Archive of Our Own. There are often various takes on crossovers like this, but the quality can vary. Some might focus more on the action elements from 'High School DxD' while incorporating the unique characteristics of 'godlike sans'. It's really a matter of personal taste when it comes to finding one you'll like.
He might fit in by becoming a teacher or some sort of mentor at the school. Since he has such great power, he could teach the students new ways of using their own powers or just general combat skills. In the process, he'd get involved in all the drama and power struggles within the school, adding a new dynamic to the story. He could also have his own goals and motives that are slowly revealed as the fanfiction progresses.
One interesting plot could be Godlike Sans using his unique abilities to help the characters in High School DxD in battles. For example, his teleportation skills might give them an edge in combat against powerful foes.
A third storyline could focus on a mystery. There are strange happenings around Sans Seraphim High School, like students disappearing without a trace. The characters from High School DxD start to investigate and uncover a dark secret that has been hidden for a long time, perhaps something related to an ancient evil that is now awakening.
Akeno is another fan - favorite. Her dual nature, being both sweet and somewhat sadistic, can be explored in different ways in fanfiction. At Sans Seraphim High School, she could be involved in a love triangle or be the key to solving a mystery related to the school's dark past.
In a Naruto and High School DxD fanfiction, there could be a scenario where the protagonists of both stories meet in a neutral dimension. Issei from High School DxD might be intrigued by Naruto's ninja skills and determination. Naruto, in turn, could be curious about Issei's Sacred Gear. They could start training together, sharing their knowledge and skills, and ultimately have to face a common enemy that threatens both their worlds.
One possible fanfiction could be about Naruto characters attending the school in High School DxD. For example, Naruto's positive and determined attitude might clash with the more complex social and power dynamics in the DxD world. He could make new friends or even rivals among the devils, angels, and fallen angels.