One possible plotline could be that Harry discovers Snape has been secretly working against him in a way that endangers his friends, and in a fit of rage, he attacks Snape. For example, if Snape was found to be involved in a plot to harm Hermione or Ron.
One possible plotline could be that Harry discovers a new dark plot by pureblood supremacists to further marginalize non - pureblood wizards. He decides to take matters into his own hands and uses his magic to fight them off. Another could be that he is pushed to the limit by the constant discrimination from purebloods and finally snaps, leading to a showdown.
Well, it could be that Hercules has done something to Percy's friends or family. For example, Hercules might have accidentally injured one of Percy's close friends during a heroic adventure. Percy, being very protective, then decides to take matters into his own hands and beats up Hercules. Also, there could be a power struggle between the two, with Percy feeling that Hercules is becoming too powerful and a threat to his own world or community.
Perhaps in some 'harry marries snape fanfiction', there could be a magical accident that binds their fates together. At first, they resist the connection, but as they get to know each other better, they find common ground and fall in love, leading to marriage. This could involve a lot of emotional turmoil and self - discovery for both characters.
In some 'Snape slave to Harry fanfiction', the plot might start with a prophecy or a magical bargain. Maybe a seer predicted that only with Snape as Harry's servant could a great evil be defeated. So, Snape, bound by this fate, has to follow Harry's commands. Along the way, they face many challenges together. Harry has to deal with the power imbalance and Snape has to struggle with his pride. Their relationship evolves from one of forced servitude to a more complex bond of respect and cooperation as they fight against the forces of darkness.
One possible plotline could be that Snape accidentally discovers Harry is extremely ticklish and uses it as a form of mild punishment when Harry misbehaves in Potions class. For instance, if Harry forgets an ingredient or causes an explosion.
Maybe in a fanfiction, Harry could be framed for something he didn't do, and Snape, believing the false accusations, smacks him in a moment of anger. This could then lead to a series of events where Harry tries to prove his innocence and Snape has to come to terms with his hasty action. Another plotline could be that Snape is under the influence of a dark spell that makes him act out of character, and Harry just happens to be in the wrong place at the wrong time and gets smacked.
One possible plotline could be that Harry discovers Snape's memories early on. Overwhelmed by the truth of Snape's love for his mother and his selfless sacrifices, Harry hugs Snape as a sign of immediate forgiveness and gratitude. Another could be in a post - war scenario where Snape is still alive, and Harry, now a more mature wizard, reaches out to Snape to heal old wounds.
One possible plotline could be that it's the result of some dark magic gone wrong. Maybe a spell was cast on Harry by an enemy of Snape's to embarrass him, and now they have to deal with the consequences together. Another could be that it's part of a prophecy that no one expected, and they must figure out how it fits into the wizarding world's future.
One possible plotline could be Harry being sold due to some dark magic plot against him. Snape then has to deal with this unexpected situation and protect Harry from further harm. Another could be that it's a part of a deal to save the wizarding world, and Snape and Harry must learn to work together in this strange new dynamic.
Another plotline could be that there is a spell or a magical occurrence that forces Snape and Harry to be close to each other. Initially resistant, Snape eventually gives in and cuddles Harry. This could then be the start of a journey where they learn to trust and rely on each other more.