The most obvious consequence would be that Voldemort would likely betray Harry. Voldemort is evil at his core, and he would probably use this opportunity to harm Harry or gain more power. For example, he could steal Harry's magic or use him as a pawn in a new scheme.
One possibility is that Voldemort could initially be amused by Harry's request. He might toy with Harry, pretending to consider helping while actually having his own evil plans. For example, he could use Harry's vulnerability at that moment to gain some sort of advantage, like getting information about the Order of the Phoenix. Or, Voldemort could see it as an opportunity to corrupt Harry further, slowly turning him to the dark side by making false promises of power and protection.
Harry could put himself in great physical danger. Voldemort might not be willing to help without exacting a high price, like Harry's own life or his magic. And even if Voldemort does seem to offer help, it could be a trap to harm Harry.
One possibility is that Harry has discovered some long - lost connection between them that he thinks can be exploited. Maybe he's found out that Voldemort has some knowledge or ability that is crucial to solving a problem. For instance, if there's a prophecy that only Voldemort can decipher, Harry might approach him for help, despite their long - standing enmity.
Perhaps Harry discovers some dark secret about his own past or powers that he thinks only Voldemort can help him understand. For example, if he finds out that his connection to Voldemort is more complex than he thought and that Voldemort holds the key to unlocking or controlling certain aspects of his own magic.
The wizarding world might be in shock. People who have always seen Voldemort as the ultimate evil would be confused. They would have to re - evaluate their views on Voldemort. Harry, on the other hand, would be in a very strange situation. He might be distrusted by some of his friends who think he has made a deal with Voldemort.
Perhaps Harry has a plan to outwit Voldemort in the long run. By seeking help, he can get closer to Voldemort, understand his weaknesses better, and then use that knowledge against him. It's a risky but potentially effective strategy, like a spy infiltrating the enemy's camp.
One consequence could be that the wizarding world falls back into chaos and fear. Voldemort would likely start his reign of terror again, targeting those who opposed him before. He might also try to seek revenge on Harry for initially defeating him.
The wizarding world would likely be in a state of shock and then celebration. People would start to see Azkaban in a new light, perhaps no longer as just a place of horror but also as the site where the great evil was finally vanquished.
The Order of the Phoenix would be horrified. They have spent so much time and effort fighting against Voldemort. If they found out Harry had asked for his help, they would likely feel betrayed. They might even try to stop Harry, thinking he had been somehow influenced or corrupted.
One possible plot could be that Hogwarts is facing a new and powerful dark magic threat. Maybe a long - lost dark wizard's spell has been activated and is slowly draining the magic from the school. The students and teachers then have to work together to find a way to reverse the spell. They might search through old tomes in the restricted section of the library and go on adventures outside the school to gather rare ingredients for a counter - spell.