One idea could be a time - travel plot where Harry, through some magical mishap, travels back in time and ends up having to work closely with a young Severus Snape. They could start off as enemies, given their future relationship, but as they face common threats in the past, they gradually develop an understanding of each other.
Another way is if there was a magical accident that forces Harry and Snape to rely on each other. For example, they are trapped in a magical realm where only by combining their unique magical abilities can they escape. During this time, they have to put aside their differences and work together. Harry learns about Snape's past traumas and Snape sees Harry's courage and determination up close, which changes their relationship for the better.
For Harry, you can explore his more mature side. Since he has experienced so much in the original series, in the fanfiction, he can be shown as more confident and less impulsive. He could also be more empathetic towards Severus, given Severus' difficult past. For Severus, his dry sense of humor and his deep - seated loyalty (even if it's hidden) can be further explored. Maybe show how his relationship with Harry changes his view of the world and makes him a bit more open.
One idea could be a story where Harry, under the influence of a powerful spell, has to live a day in Severus Snape's memories. He gets to see Snape's childhood, his unrequited love for Lily, and all the sacrifices he made. This would give Harry a new perspective on Snape.
One key element is the power dynamic. With Harry being sub and Snape dom, it creates an interesting relationship where Snape's authority and knowledge are emphasized. Another element is the exploration of their characters in a new light. Harry may show more vulnerability, and Snape may display different sides of his personality.
There is also the theme of secrecy and forbidden love. Given the nature of their relationship in the original Harry Potter series, a 'dom Harry sub Snape' relationship in fanfiction is often portrayed as something that has to be kept hidden. This secrecy adds an element of excitement and tension to the story, as they have to be careful not to be discovered by others in the wizarding world who may not understand or accept their relationship.
Another interesting one is 'Hidden Desires'. It starts with a rather unexpected encounter between Harry and Severus that sets the tone for their dom - sub relationship. The story is filled with emotional moments as they both struggle with their feelings and the implications of their relationship in the wizarding society. The author does an excellent job of building tension and then resolving it in a satisfying way.
One popular 'sub harry dom snape fanfiction' is 'A Different Sort of Bond'. It delves into the complex relationship between Harry and Snape in a way that shows Harry in a more submissive role and Snape as the dominant one. The story has great character development and explores their interactions in the magical world setting.
Another option is to check out some Harry Potter - focused fan communities on social media platforms like Tumblr or Reddit. People often share and recommend fanfictions in those communities, and you may come across some good 'dom Harry sub Snape' fanfictions through their posts or discussions.
Power dynamics is a very common theme. Harry, often seen as the dominant one, exerts his power over Lucius. Redemption is another. Lucius, having been on the wrong side, is often in a position where he has to redeem himself under Harry's influence.