To the Dark Lord:
I know that by the time you read this letter, I will be dead.
But I want you to know that I discovered your secret, I have stolen the real Soul Artifact, and I will destroy it as soon as possible.
I willingly go to my death in the hope that, when you meet your match, you will become mortal once more.
R.A.B.
"..."
"...R.A.B....who is that?"
William and Lupin exchanged a glance—for a moment—before both were left clueless.
"Perhaps someone secretly fighting against Voldemort… a revolutionary warrior?"
Lupin pondered for a moment and found a fitting phrase—yes, even though he knew Sirius had a younger brother, their relationship wasn't good, and not many cared about the latter's disappearance (except for the portrait at the end of the hallway in Grimmauld Place No. 12), so Lupin didn't realize the meaning behind the signature.
"But, maybe we could ask Professor Dumbledore, he might know a lot about… uh, underground resistance?"
Though Lupin made a good suggestion, for some reason, his wording started to sound increasingly odd.
"True, it seems there might not be any other guidance here…"
William looked around the room, finally resting his gaze on Lupin's ankle—where a shriveled, wet hand was, "…right?"
"?"
"Oh my—"
At this point, Lupin instinctively wanted to stomp on the Inferi's face, but William timely stopped him—Lupin silently pulled his foot out of the Inferi's hand, and then, the two squatted down, beginning to observe the target, which apparently wasn't about to eat Lupin, a "catch" (from the charm).
"…The target seems to be?"
William lifted the Pendant Box and dangled the box in front of the Inferi, then began swinging it left and right, so—the Inferi's head began following the direction of the Pendant Box, "Let's swing together~"
"?"
"Great, it's confirmed, it's staring at this Pendant Box."
Professor William drew a conclusion.
"Perhaps, because Voldemort put a charm on these Inferi… uh, making them subconsciously… uh, protect the Pendant Box?"
Professor Lupin raised an objection, though for some reason, he himself felt increasingly uncertain as he spoke.
"Makes sense, but don't mention this Pendant Box is fake, and even that thing is a counterfeit I pulled from history with magic—"
While not thinking Lupin's objection warranted an experiment, William still flicked his magic wand, hence, another "catch" flew out of the water, this one almost carbonized yet still capable of movement, but unsurprisingly, it seemed to prefer going after Lupin's ankle… and butt rather than the Pendant Box.
"So, the answer is obvious."
"Yes, most likely he is that R.A.…""He is a money grubber!" (in unison—not really)
"..."
"How did you come to that conclusion?"
Professor Lupin felt confused and bewildered.
"Because, this thing seems to be gold, and quite pure—"
William weighed the Pendant Box in his hand, despite being an "apparition" pulled from history, its weight was genuinely heavy—to prove his point, William knocked the Pendant Box against the second Inferi's teeth, after losing half of the decaying teeth in its mouth, a mark finally appeared on the edge of the Pendant Box.
"..."
"…Alright, I think you're right."
William absolutely ceased his obstinacy, maybe not a single greedy Inferi exists in this world (probably), "If he is indeed R.A.B.—"
"Ah, is him."
In the Headmaster's Office at Hogwarts, watching the dried corpse William physically lulled to sleep, Dumbledore appeared somewhat wistful, he took the note William handed over, and lowered his head to look at the face, which, despite drying and twisting due to becoming an Inferi, still looked young, deeply sighing.
"Who?"
"I think, there are more suitable people to explain to you—"
Dumbledore, as usual, sold the mystery, but noticed the uncommon sadness in the old man's tone, William uncharacteristically did not voice impatience, instead followed Dumbledore's gaze to a picture frame, Phineas Nigellus Black stood quietly inside it, his face expressionless.
"If you would."
Dumbledore sighed again.
Therefore, Headmaster Black turned and left, leaving the office in silence, until—a person pushed open the wooden door.
"What's the matter? That old guy was solemnly not saying a word—"
Sirius wore a layer of motorcycle jacket, resembling a millennium-era ghostly middle-aged man, but his slightly frantic footsteps clearly indicated that Phineas Black hadn't kept entirely silent, he rushed in like a whirlwind, yet when he truly set foot in the office, he halted abruptly—
"…Is it this?"
He raised his toe and indifferently kicked the Inferi's exposed shin bone with his motor oil-stained Dragon Skin Boots.
"Sirius…"
Lupin attempted to speak, his voice dry.
"…Where did you get this from?"
With a glance around, Sirius fixed his gaze on William—the reason being none other; in this room, the only person likely able to retrieve a corpse missing for decades could only be William—
"Take a look at this."
Yet William didn't answer, instead handed over the note, rewritten, because historical replicas couldn't be taken far from the scene.
Sirius took the note suspiciously and then fell into prolonged silence, as his grip on the paper gradually whitened his knuckles, the man's body began to tremble, as if scalded midway, abruptly lifting his head, his face drained of color, leaving only deep disbelief and rage—
"This is impossible!"
Sirius's voice abruptly heightened, akin to a wounded beast using a roar to intimidate a foe, Fawkes perched by the door shivered, a few golden-red feathers fell into the pocket of the ever-prepared Kabuda under the wooden frame—
"This is absolutely falsified—
"Such a crude trick! Regulus? That guy?! Since childhood, he kept boasting about 'pure-blood', the guy who willingly served Black Wizard, knelt down to polish Voldemort's boots? The coward who flaunted the disgusting Dark Mark on his arm with pride? He swapped the Soul Artifact? Resisted the Dark Lord? Willingly died? Impossible!"
Sirius took a deep breath, "Absolutely impossible!!!"