Disclaimer: JK Rowling owns the Harry Potter books and characters, of course, unless I end up coming up with any original ones. And I'm not making any money on this.
This is the oldest fiction I could find that I posted online. It was written after “Harry Potter and the Half Blood Prince” came out, but before the “Harry Potter and the Deathly Hallows.” So of course it got everything wrong about Severus Snape’s father, Tobias. It was originally posted at a Harry Potter fanfic site, and now resides at fanfiction.net.
Tobias Snape decided when he was eleven years old that he would marry a witch. That was the age when he found out that his great-granny Fudge was a witch. He'd suspected it for some time, but he finally caught her "Scourgifying" her dishes when he came home earlier than usual from school one day. He usually walked home from school to Granny's, had a snack, and then did his homework until Mum or Dad picked him up after work.
This had happened before, unbenownst to Tobias, but the other times his Granny had Obliviated the memory. This time she didn't. "The boy is more a Squib than a Muggle, anyway. He may not have magic himself, but he can definitely feel it," she thought to herself.
Things got a little dicey when she actually called herself a witch. "Magic" Tobias expected, but a witch meant devil-worship, didn't it? Well, Granny explained that, but then the real stickler was when Tobias found out he wasn't going to be a wizard.
"Your parents weren't magic, but you still ended up being a witch. How do you know I won't be a wizard? After all, it's in the family," he argued. And he was right. Some families turned up a blue-eyed child in a family of brown-eyes, or a webbed hand every so often (Tobias knew a kid at school renowned for the web between the thumb and index finger on each hand -- it was even better than the kid who could touch his nose with his tongue). The Snapes seemed to turn up a witch or wizard every third generation or so.
"That's right, Toby. That's why I keep an eye on all the grandchildren and grand nieces and nephews," she answered. "But the fact is, you're eleven now, and if you were a wizard it would show by now. You would have done magic when you were scared or angry."
This lead to a long exploration of every incident in Toby's life that could possibly be construed as inexplicable or strange to an eleven-year-old boy, including the time his mother had figured out who stole the last piece of cake from the fridge. When he had exhausted that tack, Toby made himself angry. Really angry. And tried to do magic. Granny sat there patiently the whole time, and didn't try to make him stop.
Finally, Toby called a truce. He wasn't giving up for good, but decided to give up for now. Then an idea occurred to him. Even if he wasn't magical himself, he knew that magical people existed. Maybe he could live around them.
At this point, Granny was seriously reconsidering her decision not to Obliviate her great grandson. "Muggles do not live among wizarding folk," she insisted. "It's a law."
"But you said I was more like a Squib than a Muggle," Toby insisted. "You said there are people who can't do magic who live with people who can." And then, in a burst of inspiration, something else occurred to him. "Besides, your parents were both Muggles, and you lived with them."
"Well, yes," Granny hemmed and hawed. "Muggle parents of witches and wizards do have some interaction with the wizarding world. But it's very unlikely you'd have a witch or wizard as a child. Though of course it does happen from time to time with the Snapes."
"But what if I married a witch? Wouldn't I have a better chance of having a magical child then?"
"Actually, you definitely would have a magical child then. The child of a Muggle and a witch or wizard is almost always magical."
"Then all I have to do is marry a witch," said Toby.
He continued to try to do magic for a while by making himself angry or sad, but at the age of eleven, he had a backup plan. He was going to marry a witch.