Hirajima Natsumi, Okada Mei, Hazuki Himari, and Negishi Ai arrive at a luxurious beach house. Soon after arriving, they are informed that they will be competing in a series of challenges, the overall winner of which will be deemed the "center" of Merm4id. These challenges are interspersed with gravure-type segments that feature all four unit members. Challenges include guessing what sports each member played in school, cooking omurice, drawing logos from memory, guessing smoothie flavors, a cap...