Giant Lycanroc!

Tens of thousands of years ago in the Pokémon World, a swarm of unusual meteorites fell, driving Pokémon such as Kabuto and Omanyte to extinction.

The Negative Energy contained within those unusual meteorites severely affected the Pokémon World's ecosystem. In order to survive, ancient humans began studying the fallen meteorites. Through relentless effort, humanity eventually gained a method of controlling the "Negative Energy" within them.

Based on the legends of Groudon and Kyogre's Primal Reversion recorded in mythology, humanity successfully refined this technique and bestowed the energy upon Ordinary Pokémon, achieving the "Gigantification phenomenon."

The Negative Energy within the unusual meteorites could increase a Pokémon's size severalfold, even dozens of times over. In the process, it enhanced their strength, stamina, and Double Defense. Overall, the only thing limited was their movement speed.

Furthermore, Gigantified Pokémon could absorb Negative Energy to further strengthen themselves.

It could both enhance themselves and protect the ecosystem, preventing humans and Pokémon from being completely wiped out by the effects of Negative Energy. For a time, those giant Pokémon were worshipped as guardian gods by humans and Ordinary Pokémon alike.

People regarded giant Pokémon as totems, leaving behind legend after legend. Later generations called that era the Ancient Civilization.

As time passed, the ancient era came to an end, and the Ancient Civilization was destroyed. The Pokémon World entered the medieval era. The Pokélantis Empire was one of the overlords of that age, and one of the fortunate nations to inherit the Ancient Civilization's legacy.

Relying on the unusual meteorites preserved in its ruins, the empire successfully created the Giant Guardian God, dominated the continents of Kanto and Johto, and even developed ambitions of conquering the world—before Ho-Oh wiped it out.

"Super Ancient Gigantification is rather similar to Gigantamax in the Galar Region. Both are Pokémon