Well, perhaps a plotline involves Harry having to face new and more dangerous enemies after absorbing the Hallows. Since he now has such a great power, dark wizards from all over might be after him. He'd have to learn how to control and conceal the power of the Hallows while still using it to protect those he loves. It could also lead to a situation where he has to make difficult choices about when and how to use the Hallows, as misusing them could have catastrophic consequences.
One interesting plotline could be how Harry's character develops in a different way after absorbing the Hallows. Maybe he becomes more powerful than in the original series and uses this power to reshape the wizarding world. For example, he could use the combined power of the Hallows to end the discrimination between pure - bloods and half - bloods once and for all.
One interesting plotline could be a deeper exploration of the Hallows' true powers. Maybe the characters discover new ways to use the Elder Wand, Resurrection Stone, and Invisibility Cloak that J.K. Rowling didn't fully explore in the original series. Another could be a different take on the final battle against Voldemort, with the Hallows playing a more complex role.
In certain fanfictions, Harry could use the Deathly Hallows to bridge the gap between the wizarding and muggle worlds. The Elder Wand could be used to create magical protections around muggle cities, protecting them from dark magic without muggles ever knowing. The Resurrection Stone might be used to bring back important muggle - born wizards who were killed by Voldemort, and they could then help in the fight. The Invisibility Cloak could be used to protect muggles who are in danger, like if Death Eaters were targeting them. This would create a whole new dynamic in the 'Harry Potter' universe where the two worlds are more intertwined.
One interesting plotline could be about the rebuilding of Hogwarts. After all the destruction in the war, seeing how the students, teachers, and even the magical creatures come together to restore the school to its former glory. It could involve new magical discoveries during the reconstruction process.
One interesting plotline could be exploring the untold stories of minor characters during the events of 'Harry Potter and the Deathly Hallows'. For example, how the students who stayed at Hogwarts coped with the final battle approaching. Another could be a different take on the search for the Horcruxes, perhaps with a new group of characters assisting Harry in unexpected ways.
Hermione would probably still be a main character. She'd be by Harry's side, trying to help him understand and control the power of the Hallows. She might be researching ancient texts to find out more about any potential side - effects or proper uses of the absorbed Hallows.
One common plotline is exploring what could have happened if different characters had made different choices during the events of Deathly Hallows. For example, what if Ron hadn't left Harry and Hermione in the forest? Another interesting one is delving deeper into the backstories of minor characters. Some fanfics might focus on how a particular minor Death Eater got involved in Voldemort's regime.
One interesting plotline could be how Harry's character develops in a different way after absorbing the stone. Maybe he gains new magical abilities that are not in the original story, which could lead to unique adventures. For example, he might be able to communicate with magical creatures on a deeper level or have a stronger connection to the magic within Hogwarts itself.
One interesting idea could be new magical creatures or spells that are introduced in the fanfiction. It might expand the magical world in unique ways.
One popular 'Harry Potter absorbs magic' fanfiction might be 'The Magic Absorption Chronicles'. In it, Harry discovers a new ability to absorb magic in an unexpected way, like during a battle with a powerful dark wizard. This new power changes his relationships with his friends as they learn to adapt to his growth.
In some fanfictions, when Harry absorbs the Horcrux, it could lead to a moral dilemma within him. He has to struggle with the dark influence of the Horcrux while still trying to be the good wizard he is. This internal conflict can make for a really engaging story, with Harry constantly fighting his inner demons and trying to separate his own identity from that of Voldemort's.