One possibility is that this is a misnomer or a very tongue - in - cheek title. In the fanfiction, it could be that Harry is using some new form of magic under Snape's desk that has an effect that can be humorously described as'sucking'. For instance, he could be using a spell to draw out negative magical energy that has accumulated under Snape's desk, which is causing problems in the classroom, and the spell's action makes it seem like he's'sucking' something out.
Well, it could be about Harry finding a hidden magical object under Snape's desk. Maybe it's a potion ingredient that Snape has been secretly guarding. Harry, being curious, decides to investigate further and gets into all sorts of trouble as a result.
I'd say it's quite creative in a rather odd way. The combination of characters and the strange situation described makes it stand out. It immediately grabs your attention, even if it might be a bit difficult to understand exactly what it means at first.
Some fanfictions might suggest that there are hidden portraits under his desk. These portraits could be of his family members or people he once knew and cared about. They could be whispering advice or secrets to him when no one else is around.
In this fanfiction, it could also be that Hermione is forced under the desk as part of a mystery. There could be some hidden secrets or clues under the desk that she needs to discover, but she's being forced to stay there against her will at first. As she investigates, she uncovers something that has far - reaching implications for the wizarding world.
Perhaps there could be a stack of old, hand - written notes. These notes might contain his personal thoughts on magic, or his memories related to certain spells and potions. Snape is a very private person in the original stories, so these notes could be full of secrets. For example, they could be about his past relationships or his early experiments with magic that he doesn't want others to know about.
Well, it could be about Draco realizing Harry's discomfort in the hot classrooms at Hogwarts. So, he uses his magic skills, perhaps with a bit of begrudging kindness at first, to create a special desk fan for Harry. Maybe the process of making the fan makes them interact more and start to understand each other better, slowly mending their previously hostile relationship.
Well, it could be about Sakura hiding under a desk during a pop - up dangerous situation in the Naruto world. Maybe she's using her medical skills secretly to help an injured comrade while under the desk.
One possible plot could be that Naruto and Sakura are hiding under a desk during a dangerous situation in the ninja village. Maybe they are on a mission and things go wrong, and they have to take cover under the desk while they plan their next move.
A theme could be redemption. Perhaps Snape has done something so unforgivable in the eyes of Harry that it makes Harry think Snape sucks. And the story could be about Snape trying to redeem himself in Harry's eyes. Or it could be about jealousy. Snape may be jealous of Harry's fame and Harry may sense this and thus dislike Snape.
Obviously, Harry Potter would be one of the main characters. He's the one who is likely to be under Snape's desk for some reason. And of course, Snape himself. His desk is the central location, so he has to be involved. Also, Hermione might be there. She often helps Harry out, and if Harry gets into trouble under Snape's desk, she could be the one to figure out a solution.