Definitely not. The world of Harry Potter, whether in the original works or in normal fanfiction, is centered around themes like magic, good versus evil, and personal growth. 'Drink my pee' is a completely out - of - place and unappealing idea that goes against the spirit of the series.
I'm not entirely sure what 'incrst story' specifically means as it's not a common term. It could be a made - up or very niche concept. Maybe it's a misspelling of 'incredible story' in which case it would be a story that is amazing, astonishing, or hard to believe.
The title 'little sis pussy story' is very ambiguous. It could be about a little sister's encounter with a small animal, perhaps a kitten which is sometimes called 'pussy'. Or it could be some sort of inside - story within a family or among friends where 'little sis' has an adventure or experience related to something named 'pussy' which might not be a cat at all but just a strange name for an object or situation in their private world.
I don't think the 'little sis nacked story' is well - known. There are so many stories out there, and this one doesn't seem to be among the popular or widely - spread ones. It could be a family - specific or small - group story.
There are no moral stories regarding'seducing' a little sister. A healthy family relationship is built on proper boundaries and positive interactions. For example, in a normal family, siblings might play games together, study together, or share secrets in a platonic way. But the concept in the question goes against all moral and ethical norms.
There is no information available about the 'little sis nacked story' as it stands. It could be something completely unknown or a very private anecdote. If it's a story from a book or movie, you should provide more context for me to be able to answer.