A/N : There's a strange idea that came into my head. Godric Gryffindor and Salazar Slytherin were best friends once upon a time. As any other best friends, it was possible that at some points, the two founders got drunk and made an agreement that if their line were down to one heir each, the heirs would marry and revive both lines to keep the family magic alive. The Agreements were more of a verbal thing, considering that they were drunk, but binding nonetheless because it was a Magical Agreement. As a result, the knowledge of that agreement was passed down verbally from one Head of House to his successor, a non sensical tradition that is, until the two last heirs in question who were both grew up without any knowledge of it and thrown into the chaos.

Prologue

In which Harriet Potter discovered that she was married

" Harriet, can you go first? I need to go to the loo. I'll meet you at the Flourish and Blotts. We passed them when we got here, remember?" Hagrid looked such a fetching green that Harriet nodded sympathetically. Once the gentle half giant disappeared from view, the goblin beside her said

"Heiress Potter, if I may schedule a meeting with you for tomorrow around noon?"

Harriet was surprised but nodded nonetheless.

"Sure, Griphook, but i might have to ask for a map, because I didn't remember the way from Leaky Cauldron to here, and maybe a book about etiquette to your people? I don't want to accidentally insult you."

She'd seen a couple of adults behaving downright rudely to the goblins, and thought that doing so to the creature in charge of their money was rather thoughtless. If there's anything Aunt Petunia ever taught her, it was politeness will get you anywhere. After all, that's how she'd gotten to a mutual respect with the Dursleys.

It was a rather funny story, actually. Harriet had always been intelligent for her age. Due to not having friends at school, her jerk of a cousin and possessing a photographic memory, she had always spent her time in the library, reading anything and everything that she could get her hand into. The result? A six years old who knew just about everything, and exceptionally good at accounting. Of all the subjects she'd read in the public library of Surrey, accounting was the one that caught her fancy. She devoured all books about the subject and continued on to Managerial Accounting and all related subjects. Her free times was mostly spent practicing her skills in the practice case that she copied from the books.

One day, she was home late because she got so deep into her newest practice sheet (the numbers didn't match until she found that she'd forgotten the amortization of a truck). Uncle Vernon was red in the face when she entered Privet Drive No. 4. Apparently, tax season is coming, and his usual accountant bailed, and he blamed her, as usual, almost ripping the papers in her hands until he caught the content of that paper and squinted to examine her work. He eyed her seriously, then back to the paper, where she'd finally got the number matched. Uncle Vernon might be many things, but he's a savy businessman foremost, and the numbers looked correct at a glance.

"now see here, girlie. I've been having this problem at the office. My accountant left us a huge mess. If you did the season's tax, I'll let this slide. I'll even pay you some money for your work." He offered with a strange face.

Harriet agreed immediately. It was like getting a new case without having to copy anything in the library. That evening, Uncle Vernon and Aunt Petunia cleaned Dudley's second bedroom for her, ignoring Dudley's protests, and Uncle Vernon installed a brand new computer for her. He taught her how to use the spreadsheet.

"it's much simpler than using papers. You needed to record a lot of receipts too." He explained.

The next day, Aunt Petunia told her to sit in table while she fixed breakfast for the family. It was the first time ever Harriet was allowed to sit together and eat a filling breakfast since she was in that house. Aunt Petunia said that it was because she needed her strength to do her work. The boxes were delivered by a company truck, and they were brought to her room. Harriet looked on, intimidated by the three large boxes that apparently was the receipt of Grunning's expenditure for a year, and then shook her head and rolled her sleeves. At least they kept it neatly according to the dates and bound them by months. She finished the tax in a week and Uncle Vernon looked at Aunt Petunia smugly after he checked her work.

"good job" he said and handed her a cheque with the number 25,000 poundsterlings on it.

"my last accountant's salary is 40,000 pounds a year, and you did his works in a week. But you're working from home, not full time, so I pay you the part time rate. You can spend this however you like. I'd also like for you to do my personal accounting. Your aunt will give you the bills and receipts. So you will be responsible for it. We will pay you for this too, of course."

Harriet beamed. She had never seen that much money before. Aunt Petunia took her to the bank and deposited the amount and was flabbergasted when the child, a six years old, asked the bank teller about investment account and saving accounts that can generate interests. She watched the small girl divided her money to three accounts, spending, savings and investments in trepidation.

After that, Harriet asked to be taken to buy new clothes and prescription glasses. Still dazed, Aunt Petunia complied, and actually found enjoyment in dressing the little girl up. The next few months saw Harriet being busy with school and work, and a few chores that she actually enjoyed. She had a few more clients for her booking service, and they paid weekly, contributing to her allowance and savings. Aunt Marge, her newest client, took to her suggestion of changing a few things for the kennel and enjoyed better qualities of puppies and better profitability.

When the Hogwarts Letter arrived, Harriet thought it was a joke and useless, so she threw the letter to the bin, much to the approval of her aunt and uncle, that is until Hagrid came and more or less threatened her family. Finally, with a sniff, Harriet relented to go, if only to spare her family from the terror. Her only concern was her clients, which Uncle Vernon solved by suggesting that she do on her holidays. He didn't want other people to touch his books either.

Back to the present time,

"here," the Goblin handed her a key. "it's a portkey that will deliver you to our meeting room. We will go over your accounts tomorrow and also the accounts of your husband."

Harriet stared at him uncomprehensively. "my…husband?"

the Goblin shook his head. "all will be explained tomorrow. Now, about the Goblin's custom and etiquette, we will also cover tomorrow. You need to go now."

Harriet was in pensive mood up till she returned to Privet Drive no.4. Her aunt noticed it as she helped Harriet brought her purchase up to her room.

"everything alright? Is your money enough to get your things? We can go back there tomorrow if you need to. I remembered that Lily said the bank could be connected to our non magic bank, but if you need more, we can help." Aunt Petunia said worriedly.

She might not like her niece going to a magic school. But the last five years had her seen Harriet as the daughter she never had. Harriet's chosen normal job also didn't hurt her reputation in the neighborhood. In fact, several of her friends and neighbors were Harriet's clients.

"Oh, no, apparently my parents left me a trust vault, so I used that instead of my savings. But Aunt Petunia, was I married?" Harriet wondered aloud.

Her aunt stared wide eyed at her.

"it's only that the goblins requested a meeting with me to go over my accounts and my husband's. I was confused. Was I a child bride or something?"

Aunt Petunia pursed her lips. " Not that I know of. Your mum might be strange, but I knew that she wouldn't condone child marriage for any reason. It's unnatural and vile, in any civilization, but your lot had a lot of tradition that may have something to do with that. But worry not, I haggled that Dumbledore Fellow for your full guardianship, muggle and magical that is, just for that reason. Betrothed or not, your significant other won't be able to claim you until your majority, that is 17 years old in the magical world."

Harriet hugged her aunt gladly. While they may have a rough patch in the beginning, she did pay attention and did her best to prepare her to face the world.

So, what do you think? Constructive Criticism deeply appreciated.