Sangeki Kaiiki: Shark Panic

Seven classmates reunite in their hometown for the first time in a while. They rent a recreational boat and experience a fleeting sense of freedom, but in the sea lurks a giant man-eating shark. One after another, the youths fall prey to the shark. And when the boat breaks down during the shark attack, it's a desperate situation in the open ocean! (Source: Nihon Bungeisha, translated)