From Bulbapedia, the community-driven Pokémon encyclopedia.
Miyajima is a member of Team Great Rocket from Template:Card GB 2. He's one of the Trainers at the GR Water Fort.
His deck, Whirlpool Shower Deck (Japanese: うずしおのシャワーデッキ), focuses on Pokémon. He will not duel against the player unless this uses a deck with only Energy cards.
When defeated, he gives out one Island of Fossil booster pack. Also, when defeated for the first time, he opens the door to the next room, allowing the player to reach Senta.