Forty years ago, at the age of 25, "Bertille" successfully reached the Elite Four level, becoming one of only two Elite Four Trainers in the Village of Dragons.
That same year, Bertille, alongside her fully evolved Starter Pokémon, Hydreigon, defeated two of Unova's then-current Elite Four, and successfully took the position of the third Elite Four.
But a month later, Bertille voluntarily resigned from the position, setting the record for the shortest Elite Four tenure in history.
No one knew why Bertille suddenly stepped down, disappearing completely from public view with no further news.
Even many of her former friends only knew that Bertille had returned to her hometown.
Bertille did go home. But the reason was known only to her and her great-grandmother.
Bertille's great-grandmother was the high priestess of the Village of Dragons at the time, and all the villagers respectfully called her "Wilma".
But just one month after Bertille returned, her great-grandmother suddenly passed away, and Bertille inherited the role of high priestess, taking on the responsibility of guarding the Village of Dragons.
Or rather… guarding the secret beneath the Village of Dragons.
"Bertille, now that you've become an Elite Four, I can finally take the risk. What our ancestors have guarded for generations, eventually it must return to our hands."
"Great-grandma, can't you just let it go?"
"No… I can't let it go! I've guarded the Village of Dragons for eighty years! Longed for it for eighty years… I just can't give it up!"
Unlike the somewhat hesitant and timid Bertille, her great-grandmother, though aged, was extremely forceful in character, having spent her life pursuing strength.
Unfortunately, she lacked talent, only becoming an Elite Four Trainer in her forties.
At the time, with no second Elite Four Trainer to guard the Village of Dragons, "Wilma" feared that the precious Dragon-type Pokémon and pseudo-legendary juveniles might be coveted by outsiders, so she dared not take risks.
So she stayed…
For eighty years.
Because of the Dark Energy, Wilma lived to be 120 years old, but everyone she once knew had long since passed away.
It wasn't until the rise of the newly minted Elite Four Bertille that her long-held obsession was awakened again.
The Domain!
What the Village of Dragons had protected for generations wasn't the precious Dragon-type Pokémon or the pseudo-legendaries in training, but a Domain left behind by a deceased Legendary Pokémon.
Can Legendary Pokémon die?
Yes.
The original owner of the Domain perished in war.
In most cases, a Domain vanishes with its master's death, returning to the world and nourishing it.
Later, a new being may rise through trials and once again condense a Domain; regaining the power to command the world's essence!
…But accidents always happen in this world, and this Dark-type Domain was left behind, eventually falling into the hands of Bertille's ancestors.
From then on, any of Bertille's ancestors who became Elite Four Trainers had the choice to try to obtain the Domain.
To gain the Domain meant gaining eternal life. So long as they avoided global wars or disasters, they could live forever.
What an enticing treasure!
But before Bertille, her ancestors had tried eight times, every single one ended in failure.
And failure meant death…
Because an ancient record stated: "Those who guard the Domain, within a century may produce one Legendary Seed. Whoever obtains the Legendary Seed shall undergo the trial and be chosen by the Dark Dragon."
This passage had been studied repeatedly over the years, and most interpretations were nearly identical.
The "Legendary Seed" referred to a Dark Energy seed, a crystallized remnant of the Dark-type Domain, much like the Nightmare Orb.
But perhaps because the Domain no longer had a master, the seeds it condensed had become a required condition for its inheritance.
And the ones guarding the Domain -naturally Bertille and her ancestors- could obtain the opportunity to inherit a Legendary Seed once every hundred years.
However, the Legendary Seed took fifty years to form, which also explained why the Village of Dragons could always produce a new Dark Energy wielder every other generation.
According to the records kept by Bertille's ancestors, any Legendary Seed that didn't belong to them would eventually end up escaping in various unpredictable ways, completely impossible to guard against.
Anyone who acquired a Legendary Seed, that is, Dark Energy, could take the Domain's trial and gain the favor of the Dark Dragon.
That Dark Dragon could only be the Hydreigon species, hence why every person to wield Dark Energy was always accompanied by a Hydreigon.
Naturally, Bertille's great-grandmother also possessed a Hydreigon and a Legendary Seed of Dark Energy. When she reached the age of 120, she too chose to follow her ancestors' path and attempted to inherit the Domain.
The ninth failure occurred!
Before Bertille's very eyes, the Domain unleashed a torrent of black light, devouring her great-grandmother's Hydreigon and Krookodile in an instant!
Reducing them to two pale skeletons.
As for her great-grandmother, all of her Dark Energy was absorbed as well. Perhaps her aging human body held no nutritional value, and so she was spared.
This also explained why in the underground palace, there were nine Hydreigon skeletons, and nine others belonging to different Dark-type Pokémon.
And forty years ago, that very same "Bertille" became the "Wilma" who now lay unconscious before Sato.
After all, this was a treasure guarded by her ancestors for a thousand years. Bertille naturally didn't want an outsider like Sato to obtain it.
In truth, aside from Sato, no other "outsider" who had acquired Dark Energy had ever uncovered its true secret.
Let alone the fact that, with the immense power of generations past, the ancestors of the Village of Dragons had gathered all Hydreigon lineages across Unova into their domain.
Any outsider who received Dark Energy was, by the hand of fate, bound to come to the Village of Dragons to obtain their destined Hydreigon.
Facing such deep-rooted power, the outcome for those "outsiders" was all but sealed.
A thousand years passed, and with the Pokémon League's growing influence and the steady advance of laws and order, when Bertille first met Sato, she didn't dare kill him because of his powerful background. After that, she lost the courage entirely.
Afraid to kill, she simply handed over Zweilous to Sato herself, hoping to minimize any ties between him and the Village of Dragons and to get him out as fast as possible.
…But then Sato came back.
Bertille grew resentful, which is when she tried to lure Sato to the Giant Chasm to die.
It all made sense now. But from Sato's perspective, this "treasured Domain" the ancestors had guarded for a millennium…
Was nothing but a scheduled death sentence!
Suddenly, a terrifying thought crossed Sato's mind: what if the Domain's original owner hadn't died at all, but was merely surviving inside the Domain, barely clinging to life?
What if that old record was just a trap, written to trick Bertille's ancestors into regularly offering it sacrifices, helping it recover its strength over time?
Think about it. If Bertille's ancestors had once been powerful enough to gather all of Unova's Hydreigon to the Village of Dragons, how could such strength now dwindle to just a single Elite Four Trainer?
The truth was…
The Village of Dragons had long been in decline!
But those in it were blind to the truth, while outsiders saw it clearly. And yet, in over a thousand years, not a single person had ever truly questioned the Domain's existence!