It could bring back old ways of dealing with dark magic. As Aurors, they had certain techniques and strategies that might have been forgotten. Their return could also inspire a new generation of Aurors. Maybe the wizarding world would become more secure as they use their experience to tighten security against dark forces.
One plot idea could be that Harry's Auror parents return and they have to quickly adapt to the modern wizarding world. They might be shocked by the new spells and magical devices. Another could be that their return stirs up old enemies who thought they were long gone, leading to a new battle. Maybe they also struggle to reconnect with Harry, who has grown up without them.
One interesting plot could be the main character facing a series of extremely difficult and dangerous dark magic challenges during the auror training. Maybe they have to deal with a powerful dark wizard who has infiltrated the training grounds to disrupt the training process.
One great Auror Harry Potter fanfiction is 'The Auror Files of Harry Potter'. It shows Harry's life as an Auror, dealing with new dark threats. Another is 'Harry Potter: Auror in Training' which focuses on his early days in the Auror training program.
Well, it really depends on your taste. Some fanfics in this theme might be quite interesting if you like exploring complex family relationships in the Harry Potter universe. However, not all of them are well - written. You might need to search through different fanfic platforms and read reviews to find a good one.
Hermione would be a great ally. With her vast knowledge of magic and her logical thinking, she could help Harry solve complex cases. Ron could also be an ally, using his loyalty and his own skills in combat and magic. Neville might be another one, having grown into a confident and powerful wizard, he could bring his unique skills in herbology and his courage to the Auror department to support Harry.
Well, it would probably strengthen his relationship with his friends. His friends would be happy for him to have his parents back, and it could lead to more group activities like family - style outings. For instance, they might all go on picnics together with Harry's parents.
One common theme is redemption. Harry often tries to redeem some of the minor villains he encounters as an Auror. Another is friendship. His relationships with Ron and Hermione continue to be important even in his Auror days.