Hot damn, I just thought of something really cool. So, like, I headcanon that Harry kept Parseltongue after he lost the horcrux, because it’s just really fun to imagine stuff like Harry talking to Albus Severus’ pet snake or finding a little snake in the garden and hissing a hello. Parseltongue is really neat and snakes are awesome, so it’s so feel-good to imagine that instead of being used for Dark Arts, Harry’s just using it to make convo to little scaly cuties.
Like, Parseltongue apparently transfers with the soul or whatever? So you could totally claim that Harry’s soul/magic kept/learned the skill. A skill passed down through the soul/magic could totally transfer that way.
But… do you know who also had a piece of Voldemort’s soul inside them and was speaking Parseltongue pretty regularly for a long period of time? Ginny. Ginny Weasley.
So imagine twelve-year-old Ginny Weasley going home to heal after the whole Chamber of Secrets business, and finding a snake in the garden, muttering about sunny rocks and sleep. And it scares her so badly at first, because what if Tom isn’t really gone? What if Tom’s still lurking in some dark place in her head? She freaks out and nearly doesn’t come home for dinner that day… except… then she remembers that Harry can speak Parseltongue too.
Harry had an horrible encounter with Voldemort where Voldemort tried to take his life and somehow a piece of his power transferred to Harry, so now Harry can speak Parseltongue. Maybe she just got a piece of power too when Tom tried to steal her life?
It’d be really cool to have an AU where Ginny kept Parseltongue and decided that no, I’m not going to let Tom run my life and was treated Parseltongue like the cool trick it is. And Harry is the only one who full gets it and doesn’t get a little bit uncomfortable when she drops into hissing, and maybe Harry shyly gets encouraged to start hissing back. Voldemort tried to ruin our lives so let’s stick it to him and his Slytherin ancestors, right? Yeah!
Anyway, twelve year old Ginny and thirteen year old Harry having hissing conversations at the Gryffindor table, using it to talk smack and have inside jokes, and using it to scare the heck of out any pureblood supremacists. (Who are all absolutely scandalized because Parseltongue is something Salazar Slytherin is famous for and here it’s being using for casual conversation and Quidditch commentary by a Potter and a Weasley.)
Just picture these two adorable children hissing jokes at each other in the hallways and helping each other recover from their fear and trauma.
Ginny (in Parseltongue), “<Hey Harry, let’s both stare at Malfoy breaking into laughter and hissing at each other in Parseltongue.>”
Harry, “<…That would totally freak him out. …I’m in.>”
Ginny, “<Okay, he’s noticed we’re staring now.>”
Draco, “Do you have something to say Potter?!”
Ginny, “<Laugh now.>”
Harry and Ginny burst out into enormous laughter and Draco Malfoy is furious and gets increasingly mad as Harry and Ginny crack up and hiss things like, “<Great weather we’re having today!>” and “<How about them Harpies?>”
And Draco can’t call a Professor on them because he can’t prove they’re saying anything bad (and it’s just icing on the top that they actually aren’t and he’s getting worked up over nothing).
This continues well into their relationship and into adulthood. All of the Potter-Weasley children can speak Parseltongue and have a foolproof way of having secret conversation in public. Sometimes they have to smack Jamie Sirius on the head to use English in public and tell Lily Luna to stop trying to scare people and convince them you’re the next Dark Lady. Harry and Ginny hiss at each other all throughout Ministry Events and Quidditch Events (Rita Skeeter cannot eavesdrop on them and she is furious) and to their children, lovingly telling them in this “language of the Dark Arts” to “<Behave yourselves>“ and ”<Remember to wear your jumper when it’s cold out.>“
Somewhere out there Tom Riddle and scores of Gaunts are rolling in their graves. Harry Potter and Ginny Weasley do not care.