I'm in the Ocean?

When a girl mysteriously washes up onshore, answers await. She travels inland in search of food, but instead, finds a village at the top of a cliff. As she enters, she realizes these are not the humans she knows. They are clothed in thick armor, as they've become the enemies of dangerous predators that roam the island.
Mai is taken in and enrolled in school there. On her first day, she happens to recognize her old friend, Lulu. She got in a car crash, and was never found. What could've happened to them?
Find out by reading Drako Island.