Another aspect could be that Harry's assimilation ability is a result of his experience with different forms of magic, like Parseltongue. His ability to understand and interact with snakes might be a part of a broader assimilation power. In a fanfiction, this could lead to him assimilating the magical essence of other magical creatures, enabling him to communicate with them on a deeper level and gain their cooperation in various quests.
In some fanfictions, Harry Potter's assimilation ability might be related to his connection with the magical core of Hogwarts. Since he has a deep bond with the school, he can assimilate the knowledge and power that Hogwarts has accumulated over the centuries. This could manifest as him being able to quickly understand ancient spells or magical artifacts that are related to the school's history.
One idea could be that Harry Potter's assimilation ability allows him to quickly adapt to new magical cultures he encounters during his travels. For example, in a fanfiction, he might visit a far - off wizarding community and be able to assimilate their unique magical practices and beliefs with ease, which could give him an edge in solving problems or making allies.