Snape's care for his Slytherins can also be shown through his teaching methods. He may be strict, but in fanfiction, it's often with the intention of making them better. He could give extra tutoring to students who are struggling in potions or other subjects. He understands the Slytherin ambition and tries to channel it in a positive way, like encouraging them to pursue difficult but rewarding areas of magic study.
Snape may also defend his Slytherins when they are wrongly accused. If a Slytherin is blamed for something they didn't do, Snape would use his influence and knowledge to prove their innocence. He knows the importance of reputation, especially for Slytherins, and doesn't want his students to be wrongly maligned.
Snape is a very complex character. He might use his knowledge of magic and the Hogwarts environment to his advantage. For Harry, he might keep a closer eye on him during classes, subtly guiding him without showing too much favoritism. With Draco, being from Slytherin, Snape could offer more direct advice and protection. He would have to be very careful in public to not seem overly partial. He might also use his position to give them both extra tasks or privileges that help in their development while still maintaining the appearance of fairness among all students.
One possible scenario in this fanfiction could be that Thrax, despite being a typically 'bad' virus, has a change of heart when it comes to taking care of the kid virus. Maybe he sees something of himself in the kid virus or perhaps he's just bored and decides to take on this new role. It could lead to a lot of comical situations as Thrax tries to figure out how to be a caretaker, like trying to find food for the kid virus (even though viruses don't really eat in the traditional sense) or protect it from other threats in the microscopic world.
One great example could be a story where Snape secretly protects Hermione from some dark forces in Hogwarts that the other professors are unaware of. He might use his knowledge of the Dark Arts to counter any threats aimed at her.
Some writers create it because they like to explore the relationship between two very different characters. Snape is often seen as a complex and somewhat dark character, while Hermione is bright and eager to learn. The contrast can lead to interesting storylines.
It's popular because it creates an interesting dynamic. Snape has always had a complex relationship with Harry in the original series. When Harry is deaged, it gives Snape a chance to start anew and perhaps be a different kind of influence. It also allows for exploring Snape's more nurturing side which is a contrast to his usual cold persona.
There could also be a plotline where Hermione discovers some of Snape's past traumas and in trying to help him, they form a bond. Snape, out of gratitude and a newfound respect for her, starts to take care of her like a mentor. He shields her from the harsh judgments of other Hogwarts professors and students alike, and together they work towards a better future for the wizarding world.
One common scenario is Snape protecting Draco from the other Death Eaters. Since Draco is young and somewhat naive in the ways of the Dark Arts and the Death Eater world, Snape steps in to keep him safe. Another scenario could be Snape helping Draco with his schoolwork, especially in Potions. Snape, being a master of Potions, would be able to guide Draco and boost his confidence in that subject.
One possible plot could be that Harry discovers a time - traveling accident has brought baby Snape to his present. Harry, being the kind - hearted person he is, takes it upon himself to care for the baby. He has to figure out how to feed the baby, keep him clean and comfortable. Maybe he also has to protect baby Snape from any threats in the wizarding world that might target Snape even as a baby.
One interesting plot could be that Hermione discovers Snape is ill or injured in a post - war scenario. She uses her vast knowledge of magic to nurse him back to health. During this process, they start to understand each other better. Snape, who has always been a rather aloof and misunderstood character, begins to open up to Hermione, sharing his past traumas and the reasons behind his actions in the war.