"Ah, I thought you'd be a little more surprised, like asking who this 'idiot' suddenly chiming in is..."
"Okay, so who are you?"
"The one who killed Voldemort."
"..."
For the first time since Regulus appeared, an expression of doubt appeared on the man's young, tense face. "Is what you're saying true? You really killed that... immortal Dark Lord?" The silver-white ghost began to tremble, and even its color seemed to fade a bit.
"The second time, it was me—" William nodded and sat down for a drink of water.
"The second... I knew it, I knew I didn't destroy the means for his resurrection..."
Regulus Black was dazed for a moment, then let out a long sigh, "So, there was a first time? Then who was it the first time..."
"It was Potter, Harry Po—" Sirius answered reflexively.
"Actually, it was rebounded due to oversight. After all, casting a Killing Curse on a baby is ethically and morally wrong, even for a Dark Wizard... well, the reason was that the protective magic Lily Evans cast for Harry Potter rebounded the Killing Curse, so actually Voldemort killed himself—"
Seeing that no one was responding, not even Lupin, who usually played along, William decided to stop his odd remarks.
"...Who are these people you're talking about?"
Evidently, during the first Wizard War, Regulus, who spent most of the time in school and only discovered Voldemort's true nature a year after graduation, wasn't familiar with these two names that suddenly popped up.
"Harry is James's child, who is also my godson—"
Sirius began to help with the introductions, his tone somewhat stiff, clearly still not sure what expression to use while facing his long-lost brother, "Lily is James's wife... James Potter—Gryffindor's Chaser—"
"Oh—the curly-haired one."
Finally, Regulus nodded. Being two years behind Sirius, he obviously didn't know much about the senior years, but as the Seeker for the Slytherin Quidditch team at the time, he was quite familiar with the Chaser from their rival house. Familiar to the point where he would curse at the photo for half a minute during every practice.
"Surprising, but not unexpected, given they didn't kill the Dark Lord—"
"I also didn't... not completely."
William nodded, finally deciding to steer the topic back on track. "Though I did indeed pulverize the Voldemort you knew, the presence of multiple Horcruxes makes his survival ability akin to that of a tardigrade, for instance, recently—he's emerged again. That's why I've pulled you from the Illusory Realm."
"...Because of the Horcruxes."
"Yes, since we don't know what method you used to destroy the Horcrux, or if it was effective, we need to confirm—"
"I gave the Horcrux to Kreacher, to have it destroyed."
"...You entrusted something so important to a House-Elf? That guy?!" Sirius stood up, utterly shocked.
"Who else then? Who should I have given the Horcrux to? Bella?"
"You should have come to me..."
Sirius paused, realizing something—in those days, their relationship could be described as antagonistic rather than family.
In 1979, the war was almost in its final stages. The relationship between regular wizards and Death Eaters had reached a boiling point. Sirius even felt ashamed of having a brother by blood association—let alone helping him. Even if Regulus had told him the truth, Sirius's reaction would likely have been—
Death Eaters' schemes are truly cunning and disgusting... that sort of thing.
"So, Sirius, go with Lupin to find that Kra, Kre..."" "Kreacher." "That House-Elf, and bring back Slytherin's Pendant Box."
William interrupted the gradually awkward and anxious atmosphere, and started assigning tasks, "Regulus... you can probably wander around the campus, see your range of activity now as a ghost—don't worry, not many people at the school will remember you."
Then he turned to Dumbledore, "And then, Dumbledore, we need to synchronize our information."
...
"...That's about it, Helbo's identity is truly astonishing, the Divine Envoy Hermes—I originally thought these things were just Muggle fantasies, but it turns out these gods might actually be old wizards playing role-playing games and ancients imparted to them—"
William took a sip of the bitterly strong tea, soothing his throat, which felt a bit dry from saying too much at once.
"...Sounds like a stage play script."
"Yes, and quite a cheesy one at that, after all..."
"...No one could have imagined that these events would involve such a massive organization..."
The words were heavy, but Dumbledore's expression remained fairly relaxed. He took a sip of the liquid in his cup, which was more accurately described as honey with a splash of tea leaves, and continued, "But there are still many points of doubt, such as—why a group like that would choose to cooperate with Voldemort."
"Why?" William asked, a bit puzzled, holding his teacup.
"After all—" he paused, "though Tom was indeed the most powerful wizard—Dark Wizard I've ever known, I can't see the necessity in this collaboration."
Just about to say Voldemort was the most powerful wizard, Dumbledore reconsidered upon remembering the strange creature sitting before him.
Claiming someone as the most powerful is too rash a statement.
"Oh, it's truly touching, thank you for not putting me in the Dark Wizard category—"
"You're welcome."
"Perhaps, there's something we are not aware of, given that everything happens for a reason. If there's something about Voldemort that allows them to achieve their goals, then everything becomes clear. And actually, I always have a premonition..."
William rubbed his nose, "These guys are probably after me." For some reason, William felt a strange sense of imminent danger swelling inside.
"Your premonitions often carry weight, William."
Dumbledore nodded, clearly not categorizing William's 'premonition' as an 'unreliable prophecy' but considering it as a somewhat important clue, beginning to ponder it carefully.