Participating in the island's activities, like the Islamon game, is recommended to unlock extra content even if you aren't focused on achievements.
Use software like WinRAR or 7-Zip to extract the contents. Summer.Pockets-DARKSiDERS.rar
Includes a "Restart" mechanic that triggers after clearing two routes, affecting specific CGs and items like bait for the "Islamon" minigame Steam Guide. Technical Handling (The ".rar" Archive) Participating in the island's activities, like the Islamon