Pororo: Underwater adventure

"I want to be a hero like you!" Pororo and his friends went on an underwater adventure to become heroes who protect the sea, following Captain Murlock who leads Red hunters, the guardian of the sea. However, the monster Sitter swallowed the entire submarine of Pororo and his friends, and Pororo and Cron, who managed to be rescued with the help of Captain Murlock, decided to join Red hunters in their final mission to save their friends who were taken away by Sitter. However, the secret girl, Marin, appears and begins to sabotage their operation, revealing the real secret hidden in the sea... Will Pororo and his friends be able to solve mysterious secrets and become true "Sea Guardians"?