"So you know what's wrong with her?" Albus asks. His words are direct not harsh yet still Aberforth whirls his head around to snap at him. That there's nothing wrong with Ariana. But there is something wrong with her no matter Aberforth's protests. Ariana can't help it and neither Albus or Aberforth are able to help her but maybe Harrison Evans can.
Thankful Harrison interrupts Aberforth before Albus' brother gets the chance to protest. "She's an Obscurus." Harrison says simply.
Albus has always prided himself at being one of the best students- Perfect and Head boy despite that curtain incident- at Hogwarts. He also had been one of the brightest to graduate Hogwarts. So there isn't much Albus doesn't know.
What a Obscurus is falls into the small category Albus doesn't know. He hasn't even heard of the word before today. He leans forward from his seat.
"When a magical child for some reason - usually through abuse either physical or psychological - repress their magic, their own nature, he or she will develop a parasitical magical force inside of them. A Obscurus."
"There's a parasite in Ariana?" Aberforth asks Harrison before Albus even gets the chance to open his mouth.
Harrison nods. Aberforth gets that look on his face that means he wants to runaway from the world, from Albus, and play with his goats and Ariana.
"Most Obscurus die before their tenth birthday." Ariana was fourteen now. "Your sister is special case."
This time Albus doesn't give Aberforth the chance to ask the question on their minds. Despite what his brother thinks Albus does care for Ariana even if he doesn't always show it.
"Have there been any other special cases?" He asks Harrison- Harry was the name he preferred but to be honest Albus preferred using Harrison.
"Yes. His name was Credence Barebone. He was killed by aurors instead of by his Obscurus." So Ariana would have been murdered instead of permanently living in a wizarding hospital. Suddenly it's hard for him to shallow.
"Why are you helping us? Helping Ariana?" Aberforth asks as Albus is sorting out his thoughts.
Harry gives them smile. It doesn't reach his sad eyes that are the color of the unforgivable Avada Kedavra. "Because I could have been one too."
A/N: Originally posted on ao3 under the pen name youngjusticewriter. Part one "The advantages of foreknowledge and the disadvantages." series.