Disclaimer: J.K. Rowling owns Harry Potter 24 hours a day 7 days a week.
And folk tales belong to humanity.

I think that if the story is a collection of finished one-shots, then its proper status should be "Complete".
So, I've marked this collection as "Complete", but I plan to add more chapters.

Acknowledgements:
I use the setup from the story collection "Muggle Fairy Tales Are Mad!" by Meltha.
I asked her (or him?) for permission more than 1.5 months ago and did not receive any answer.
I believe I've waited long enough and have moral right to go ahead.

CHAPTER 1
Kind Stepmother

Chapter summary:
Hermione tells the boys a Russian folk tale and Harry decides that the memory of a certain boggart could be a good Patronus memory.

Polyjuiced Harry, Ron and Hermione went into muggle grocery store.
While Harry and Hermione picked up the food for dinner, Ron stopped at the bakery section, looking at the cakes.
"Honestly, Ron", said Hermione, "You are thinking of cakes now?"
Ron smiled guiltily and said softly, "Today is mom's birthday".
"Oh, sorry", said Hermione, "You know, why don't we buy a cake as well? We can afford it once in a while."

That evening, after dinner and cake were eaten, they sang 'Happy Birthday'.
After that Ron looked at Hermione and said, "And, to finish the celebration properly, how about one of your weird muggle stories?"

"Oh, well, I suppose ...", said Hermione, "Hmm-m, you know, I'd like to tell you one of Russian tales, for a change."
"Russian?" asked Harry.

"Yes ... one of our common acquaintances sent me a book of Russian folk tales. As a gift for my birthday", said Hermione in a slightly tense tone, looking at Ron warily.

"You mean Victor?" Ron said, "Ah, it's nice of him."
Harry noticed with satisfaction that Ron was able to say Victor's name, showing nothing but polite indifference.
And, judging by Hermione's smile, he scored a few extra points in her esteem.

"OK, let it be Russian fairy tale", said Harry.
"Actually it's not a fairy tale" Hermione said.
"It's not?" Harry said.

"No, it's of so-called 'morality tale' kind", Hermione said, "And the tale is 'Kind Stepmother'".
"Huh? I thought in your tales stepmothers are always evil", Ron said.
"Well", Hermione bit her lip thoughtfully, "This is an exception. I really cannot recall another case of stepmother being not evil."

"Does this tale start with 'Once upon a time'?" Ron asked with exaggerated concern.
- Yes it does.
"Then it's OK", said Ron with exaggerated relief.
He and Harry exchanged glances and winked to each other.
Ron took a breath and said, "Once".
Harry said "upon".
Together they said "a time" and motioned for Hermione to continue.

Hermione huffed and tried to look indignant, failing miserably.
She chuckled and continued,
- Beyond thrice-nine lands in the thrice-tenth kingdom there lived a Tsar with his wife-Tsarítsa and a little daughter-Tsarevna.

"Thrice-what?" asked Ron.
"Beyond thrice-nine lands in the thrice-tenth kingdom", repeated Hermione.
"Which means beyond 27 lands in the 30th kingdom?" asked Harry.
"Well," Hermione said reflectively, "of course, the apparent meaning is 'in a faraway land', but one does wonder, why such precise numbers are used.
Eh, anyway, it's a common phrase in many Russian tales, so, let's just go with it."
"Fine", said Ron.

- Happily they lived together, but then it so happened, that Tsarítsa got sick and died.
The Tsar had grieved for a while, but it could not be helped.
A few years had passed.

One day the Tsar said to his young daughter, "Daughter dear, I'm sorry that your mother has died, but it could not be helped. And now I do need a wife."
"I understand," said Tsarevna, "but, daddy dear, would your new wife love me like a mother?
Please, let me choose the wife for you."

"Huh," said Ron, "it actually makes bloody sense."
Hermione stopped for a moment, nodded and continued,
- The Tsar agreed and in a chosen day all eligible maidens came to the palace.
They stood in a row and Tsarevna walked slowly along them.
Every maiden, she passed by, remarked to her,
- Oh, what a pretty girl!
- What a clever girl!
- Such a well-behaved girl!
And so on.

One maiden looked at the girl, sighed and shed a few tears, "Oh, poor child, so young and already an orphan."
The girl took her by hand and led to her father, "Daddy dear, here is a good wife for you, who will love me like a mother."

"The End", Hermione finished and smiled at Harry knowingly.
Ron opened his mouth, going to complain about absence of 'happily ever after', but looked at Harry and stopped himself.

And Harry felt like something warm was rolling in his chest.
He realized why on this day, on the birthday of Ron's mom, Hermione chose this tale.
Yes, Mrs. Weasley indeed loved him like a mother.

Later that night he lay in bed, without sleep, going through memories again and again.
Her birthday gifts, her meals, all the little things which parents give to kids without thinking.
Her annoying overprotectiveness … because she cared about him.
Her animosity towards Hermione, while she thought that Hermione dumped him for Victor.

Her boggart - dead bodies of her children and Harry's among them.
This last memory, Harry decided, would be a good happy thought, good for Patronus.

How would you pronounce: Rev-U?

AFTERWORD

I've read this tale ("Добрая мачеха") when I was a child.
Now I cannot find this tale on the web (neither in Russian nor in English); so, I translated it from memory.