There is a small inaccessible island directly southeast of the main island that can only be seen on the Town Map.
DANGER! FAST CURRENT!
Fishing and surfing prohibited!
The island has a small town that is rather important to the player as its shop is the only place where players can obtain rare Poké Balls not produced in Kanto by Silph, such as the Timer Ball, and several items only available in Johto and Hoenn, such as Moomoo Milk and Lava Cookies. In addition, Rage Candy Bars are suggested to be sold here, hence Bruno's visit to the island; however, they are sold out, making Bruno leave empty-handed.
Boon Island for Two (Japanese: ひとりより ふたりの ゆうぎじまFriendship Island for Two)