"I'll send you the business plan tonight." Regulus waved goodbye to Severus, watching him disappear into the green flames of the Leaky Cauldron's fireplace.
Regulus, who had just painted a grand picture for someone for the first time, let out a long breath.
Flourish and Blotts.
Regulus picked up a copy of Professor Wendyk's *Curses and Counter-Curses* and casually put it in his shopping basket.
Sirius should like this book.
There was also a Transfiguration book that mentioned Animagi – Sirius and the others hadn't thought of using the Animagus transformation to help Lupin yet, and he didn't want to steal that honour from them – he would give this book to Sirius and let the small group figure it out themselves.
"Hello, sir, I need a copy of *The Invisible Book of Invisibility*," Regulus said to the manager who was tidying shelves on a ladder.
Like all Wizards intending to do things on a dark and stormy night, he desperately needed to study all sorts of knowledge about invisibility, such as the Disillusionment Charm being just the basics, and requiring various methods to evade detection, and so on. He had seen this book recommended in *Transfiguration Today*.
"Oh dear..." The manager showed a helpless expression. "Someone actually wants that book... Listen, young man, we stocked two hundred copies before, and they were absolutely the worst – those books were so expensive, and we never..."
"Alright, we can't find them anymore, we've tried everything – Revelio, Accio... If you can find one, you can take it for free."
"I swear I'll never stock those books again," the manager shook his head, shaking off the unpleasant memories, and muttered to himself, "Never again..."
Regulus looked at the rows of bookshelves that reached up to the high ceiling and couldn't help but rub his forehead.
Hmm, it seems this book is indeed very effectively invisible...
Since he was already here, he walked around the bookstore and bought several books, activating his "Stealth" skill, and kept silently chanting *The Invisible Book of Invisibility* in his mind.
Perhaps his earnest thoughts generated magic, or perhaps it was the effect of "Stealth". He suddenly saw some distortion in the light on the bookshelf in front of him, just like at his home at Number 12 Grimmauld Place, and a book forcefully squeezed its way out from beside the other books on the shelf, appearing before his eyes.
*The Invisible Book of Invisibility*
He opened it, and on the flyleaf was written—
"Congratulations on finding this book. The first element in seeing through invisibility is invisibility itself."
The manager nearby almost fell off the ladder.
...
This book was simply a perfect guide to Invisibility—
Making oneself invisible, making objects invisible, hiding the traces of invisibility, finding the traces of invisibility...
It was like training a spear while also training a shield, and occasionally pulling them out to practice contradicting each other. Or rather: it was like training a programmer to perform cyberattacks while also training him to improve cybersecurity.
Every time Regulus finished a new chapter, the book would inexplicably disappear from his bedroom, waiting for him to rack his brains and use every method to find it again.
And Sirius and Regulus also started a new game: they, along with the book, would play "hide-and-seek" with each other.
One day, they were very surprised to see the book appear on his desk.
"Kreacher saw the book under the bed and brought it up," Kreacher said.
The House-elf's magic was truly amazing! They seemed to have some peculiar contractual relationship with the house, knowing almost everything within it like the back of their hand.
Warm-up time for the day's dueling game.
"Kreacher is so cool, look at his magic, many adult Wizards can't do it," Regulus said, casually flicking his wand, "Expelliarmus!"
"He's just a House-elf," Sirius said noncommittally, waving his wand with ease, "Protego!"
"I can't believe it, you sound just as heartless as Mum, like a cold stone," Regulus said mercilessly, "Petrificus Totalus!"
"He doesn't have his own thoughts at all, he just blindly obeys—" Sirius tried to retort, "Stupefy!"
"Who says he doesn't have his own thoughts? He's better to me than he is to you," Regulus dodged nimbly, even having time to spread his hand, "Accio Wand!"
"His dream is to have his head chopped off and hung on the wall—Depulso!"
"That's his way of showing love—Leviosa."
Sirius, defeated.
...
What puzzled Sirius even more was—Regulus was clearly humble and polite, even quiet, at school or with others, so why did he have so many cutting remarks every time he was just with him?
He couldn't even win an argument against his own brother?
Don't ask; if you ask, it's because a certain Muggle said it.
Things like "Books are the ladder of human progress," "Everything we hear is an opinion, not a fact," "Do your own thing and don't mind others," and so on, all sounded logical and profound.
It seemed he would have to take a look at these Muggle books.
But overall, he had a very happy summer—
Ever since he heard the dialogue between Regulus and Snape in front of their family tapestry, he was absolutely certain that Regulus was different from their parents and was someone who shared his ideals.
And with Regulus, Mum and Dad's favourite, covering for him, and Regulus, Kreacher's favourite, speaking well of him, he found that his life at home had more than doubled in comfort, and he hadn't triggered a single grounding punishment – he suspected the diamonds they gave their parents also played a role in this good life.
Well, his favourite person at home was also Regulus...
At a certain moment on a certain day during the summer, Sirius's mind finally learned to change direction; he finally admitted that Kreacher did have redeeming qualities and wasn't completely inflexible (Kreacher helped Regulus by turning a blind eye to some small things), and Slytherin wasn't that bad either; his own prejudice against Slytherin was no longer valid.
...
On the roof.
"You really are a Slytherin," Sirius commented with a touch of respect after hearing Regulus placate their mother in various ways to get her to agree to him inviting his Gryffindor classmates over.
"What's wrong with being a Slytherin? Although I'm a Slytherin, my name Regulus – that belongs to the constellation Leo," Regulus said shamelessly, "Even according to Muggle astrology, my birthday is in Leo."
"My Leo component is so high – wouldn't it be completely unsurprising if the Sorting Hat sorted me into Gryffindor?"
???
As soon as he said this, Sirius's face was full of question marks.
"Maybe I'm even a descendant of Ravenclaw? The evidence is right here," Regulus said slyly while using magic to comb the eagles' feathers, "I also consider myself loyal and honest, kind and friendly, Hufflepuff shouldn't refuse me either—"
"Just tell me, where would the Sorting Hat sorting me be unreasonable?"
I've never seen such a shameless person – Sirius couldn't help but laugh.
The two brothers looked at the burgeoning amusement in each other's eyes and burst out laughing together.