Maybe in the fanfiction, a new dark wizard rises to power even more powerful than Voldemort. He creates a reign of darkness by spreading a dark plague across the wizarding world. This plague turns wizards into his mindless slaves. Harry's son or daughter has to step up and find a cure while also leading a resistance against this new dark force. They might have to travel to far - flung places in the wizarding world to find the ingredients for the cure and allies to help in the fight.
A plot could involve a group of dark wizards who manage to steal the Time - Turner and change the past in such a way that Voldemort won the war long ago. As a result, the wizarding world has been living under his reign of darkness for years. A young, brave wizard discovers what has happened and tries to go back in time himself to fix the changes and restore the original timeline where good prevails. Along the way, he has to face many challenges and dangerous dark wizards who are protecting the altered past.
It could be a concept where the normal rules and values of the Harry Potter universe are turned upside down. Darkness reigns means that the dark side of magic has become dominant. This might include the dark creatures like dementors being used as enforcers by the bad guys. The main characters would then have to find ways to fight back against this all - encompassing darkness, perhaps by uncovering long - lost magic or forming secret resistance groups.
A story where Harry is a detective in a modern - day city and has no connection to magic or the Potter - like world at all. This would be an example where he is not part of a Potter fanfiction as it completely deviates from the Potter universe's concepts.
Sure. One possible plot could be that Draco Malfoy gets a restraining order against Harry Potter after a particularly nasty duel. Malfoy claims that Harry's use of magic was too aggressive and he feels threatened. The story could then revolve around how this affects their relationship at Hogwarts, and how the wizarding community reacts to such a strange situation in the middle of their magical world.
I'm not sure specifically as there could be many different interpretations in a fanfic. It might be about a period in the Harry Potter universe where dark forces gain more power than usual, perhaps with Voldemort or other dark wizards having a stronger hold on the wizarding world. Maybe it focuses on how the characters like Harry, Hermione and Ron deal with this new and more dangerous situation.
One possible plot could be that a new character in the fanfiction, who is secretly working for Voldemort, tries to steal a line from Albus Dumbledore's private notes. This line is believed to hold the secret to defeating a certain dark curse. The character tries all sorts of sneaky ways to get to the line, like infiltrating Hogwarts under a false identity and spying on Dumbledore.
In a fanfic, there could be a prophecy that when the falling petals of a particular magical flower turn black, it signals the arrival of a great evil. A group of young wizards and witches, including some of our favorite Harry Potter characters, set out to find the source of this dark omen. Along the way, they encounter various challenges and mysteries related to the falling petals. The petals' changing color could be a sign of a powerful dark magic at work, and they must find a way to stop it before it's too late.
Since we don't really know what 'pein' is precisely, it's difficult to give a specific example. But generally, if 'pein' was a new type of magic or a new character, an example could be a story where Harry Potter has to face a challenge related to 'pein' magic that no one in the original books has encountered before.
One example could be a fanfiction where the duo is Hermione and Draco. The story might be about how they are forced to work together on a secret project in Hogwarts and gradually change their opinions of each other.
Since it's a Harry Potter fanfic, it's likely that Harry Potter himself would be one of the main characters. He'd probably be at the forefront of any resistance against the 'reign of darkness'. Hermione Granger would also be a key character as she is known for her intelligence and would be valuable in coming up with plans. Ron Weasley too, as Harry's loyal friend, would be involved.
One possible plot could be that Harry Potter himself is tricked into a magical contract that binds him to a devil bride. He then has to figure out the nature of the dark magic used and find a way to break the contract before it's too late. Along the way, he might face challenges from the dark forces behind the devil bride and also deal with the reactions of his friends who are both horrified and confused.