A simple idea could be that Snape is framed for the bomb explosion. He has to clear his name while also trying to find out who the real culprits are. This could lead to a lot of tension between him and the other characters, especially those who have always been suspicious of him.
The fanfic could start with Snape sensing something amiss in the castle. As he investigates, he stumbles upon a group of individuals planning a bomb explosion. Snape then has to use his magic in creative ways to disarm the bomb or at least delay the explosion. Along the way, his relationship with other characters could be explored further. For example, how Harry Potter and his friends view Snape during this crisis. Will they trust him? And how will Snape's actions during this event impact his standing in the wizarding world?
One idea could be that a vampire infiltrates Hogwarts and Snape, Draco, and Harry have to put aside their differences to deal with it. Maybe the vampire has a special connection to the dark arts, which Snape is intrigued by while Draco is initially tempted by the vampire's power, and Harry is just determined to protect the school.
One idea could be a story where Draco Malfoy starts to question his family's beliefs after Severus Snape secretly gives him some old potions notes from a Muggle - born wizard. Harry Potter could accidentally discover this new side of Draco during a late - night encounter in the library.
One popular theme is Snape's redemption. Many fanfics explore how he tries to make up for his past mistakes and his actions that were misinterpreted. Another theme is his unrequited love for Lily, which is often expanded upon in fanfics, showing his deep - seated emotions and how it influenced his life.
One possible fanfiction could be about Hermione discovering Snape's hidden past and his true motives. She might initially be skeptical but as she delves deeper, she realizes that Snape was more complex than she thought. For example, she could find out about his love for her mother's friend Lily and how that influenced his actions throughout the series.
One idea could be a story where they are forced to work together on a dangerous mission for the wizarding world. They start off distrusting each other but gradually come to respect one another as mates. Harry's courage, Snape's cunning, and Lucius's ambition could combine in interesting ways to overcome the challenges.
I'm not sure specifically about a fanfiction with all those elements. There are countless Harry Potter fanfictions out there, so it might exist. You could try searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own.
One possible fanfiction could be about Severus Snape discovering a new magical creature on the Hogwarts grounds and Harry Potter getting involved. Maybe it's a creature that has the power to heal dark magic wounds, and Snape initially wants to keep it a secret for his own reasons, but Harry stumbles upon it. They then have to work together to protect the creature from those who might want to use it for evil.
An idea could be that there is an ice cream that can show memories when you eat it. In the fanfic, Harry Potter could eat this ice cream and relive some of his forgotten or suppressed memories about his parents. This would add an emotional depth to the story and also be a unique use of the ice - cream concept within the 'Harry Potter' world.
One possible plot idea could be how Snape deals with the physical and emotional changes during the pregnancy while still trying to maintain his role at Hogwarts. Another could be the reactions of other characters like Harry, Hermione, and Ron when they find out.