Another plotline might be that it's part of a spell gone wrong. Maybe Snape was trying to cast a spell on Harry for some reason, like to test his magical resistance, and instead it results in uncontrollable tickling. This could lead to a situation where Harry has to find a way to reverse the spell with Snape's begrudging help.
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.
One possible plotline could be that it's a moment of unexpected playfulness between Draco and Harry. Maybe they are in a truce situation, and Draco, in a moment of light - heartedness, decides to tickle Harry as a form of friendly teasing. It could be a way to show a new side of their relationship, moving away from their usual rivalry.
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.
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.
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.
Well, one possible plotline could be that Snape is examining Harry for some sort of magical ability or deficiency that he suspects. Maybe he's trying to figure out why Harry has such an affinity for certain spells. Another could be that Snape is examining Harry as part of a school investigation, perhaps related to some mischief that's been going on. And it could also be that Snape is secretly examining Harry to protect him from some hidden danger in the wizarding world.
In some stories, the reason for Snape helping Harry could be related to a prophecy or some long - hidden magic. The plot could involve Snape gradually changing his view of Harry as he helps him through the mpreg. They might develop an unexpected bond during this time, and together they face challenges from other characters who either don't understand or oppose what's happening to Harry.
The letter might be a summons to a secret wizarding council. Harry Snape's journey to deliver it could involve him facing his own inner demons as well as external obstacles. He might have to pass through dangerous terrains and encounter magical beings that are either trying to stop him or help him depending on their own agendas. As he gets closer to his destination, he discovers more about the true nature of the council and his role in the wizarding world.
One possible plotline could be that they keep their marriage a secret to avoid the chaos it would cause in the wizarding world. They might have some sort of deep understanding that developed over time, which led to their union. Another could be that they got married for some sort of strategic reason, like protecting each other from certain threats.
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.