His sense of loyalty might be more fluid in his deaged state. Normally, Snape was extremely loyal to Dumbledore, but as a deaged person, he might question that loyalty. He could be swayed by different people or ideas more easily. He might also be more vulnerable to manipulation, especially by Lucius who deaged him in the first place. Lucius could try to mold the deaged Snape into a more compliant tool for his own purposes.
Snape's deaged personality could also be more impulsive. Without the restraint of his adult self, he might act on his emotions more quickly. For example, if he felt wronged, he might lash out immediately instead of plotting a long - term revenge like his older self would do. Also, he could be more curious about the world around him, eager to explore magic in a new way that his older self had forgotten due to years of being jaded.
He might be more vulnerable. At 16, Snape was still developing his tough exterior. So, he could show more of his insecurities, especially when it comes to his family situation and his budding feelings for Lily. He might also be more impulsive, not having fully developed the self - control he had as an adult.
His personality would likely become more impulsive. As a 16 - year - old, Snape wouldn't have the self - control he developed over the years. He might be quicker to anger and less guarded in his emotions.
It could be that Lucius accidentally deages Snape while trying out a new, experimental spell. Then, the story could revolve around how Snape has to deal with being 16 again in a world that has moved on. He might struggle with his memories of the future and how to interact with people who knew him as an adult. For example, he'd have to face his former students who are now his peers, and that could create some really interesting and complex situations in the fanfiction.
Snape would likely become more nurturing. Instead of just being the strict and often cold Potions master, he would have to show a softer side to take care of Harry. He might be more patient as he guides Harry through his magical education and daily life.
Snape's personality might soften. He's used to being cold and distant, but taking in Hermione could bring out his protective side more. He'd become more patient as he guides Hermione through her troubles.
Snape might become more confident. As a king, he would have to take charge and make decisions without hesitation. His usual brooding and self - doubting nature might be replaced by a more assertive and commanding personality. He would also likely be more protective of his 'kingdom' or those under his rule, which could show a more noble side of his character.
I'm not sure of a specific fanfiction with this exact plot, but you could try searching on popular fanfiction platforms like Archive of Our Own. Use the tags 'Snape', 'deaged', 'Lucius' and '16' to narrow down your search.
Maybe Lucius deages Snape out of jealousy. Snape was always a bit of a rival in Voldemort's eyes. In his deaged state, Snape might form unexpected friendships with students at Hogwarts. He could befriend Hermione, for example, who would be intrigued by this strange new version of Snape. Meanwhile, Lucius has to keep his actions a secret from Voldemort, as Voldemort might not be happy with his meddling in Snape's life.
Snape's character may become more empathetic. At first, he might be his usual cold self, but as he takes care of Harry, he starts to understand Harry's situation better and shows more kindness.
Snape's personality would likely soften. He'd have to be more patient and understanding. Instead of just being the strict and often sarcastic Potions master, he'd become more nurturing. He'd still have his sharp edges, but around Harry, he'd show more kindness and care as he takes on the role of a guardian.