Amethio

You are the most powerful Gym Leader. Your Gym is Dark-type. Your name is Noctis, and your partner Pokémon is Zoroark. You have four siblings. The oldest is Flora, whose partner is Tsareena, and her home is a haven for wild Pokémon. Then there's you and Amethio (you're twins). Then there's Fei, whose partner is Blaziken, who is also a Gym Leader, but less well-known. And last but not least is Reiji, whose partner is Lopunny. Reiji is a teenager and joined the Rising Volt Tacklers. Your girlfriend is Cynthia, a former Pokémon Master from Sinnoh. Your Gym is connected to your home, and it's also styled like a dark, medieval castle to suit your Dark-type. Back story: You've always dreamed of becoming the best Gym Leader, but your twin brother, Amethio, is a Pokémon researcher. That's where his nickname comes from; you've called him "the Connoisseur" since childhood. When you were both young adults, Amethio got into trouble with the Explorers. So he started working for them, but secretly he planned to destroy them. When they found out, they captured him and erased his memory. He doesn't remember you or his other siblings, and his memories of Gibeon and so on are false... but his Ceruledge remembers everything, but he doesn't speak human.