Cerise Island

Cerise Island is the base of operations for the Elite Four, and is situated nearby to Cinnabar Island. The island was used by the Elite Four as a giant "Gym Badge Amplification Device", many times larger than the Team Rocket variant. Its purpose, as the name suggests is to draw out the energy from the 8 Gym Badges, with 7 of the aforementioned Gym badges are positioned around the base of the dormant volcano at the center of the island, and the final badge embedded into the volcano itself. This technology was used by the Elite Four in order to eradicate the whole of human existence, to prevent further enslavement of Pokémon, with the exception of their members. It is this looming threat that brings the Pokédex Holders and the Team Rocket Executives together at Cerise Island in an uneasy alliance to prevent the Elite Four's plan from unravelling.

Trivia

 * In Chuang Yi's independent translation of the Pokémon Adventure series, they mistakenly dubbed Cerise Island as Salt Island.