Mamori Tokonome, a shy 16-year-old, is used to being taunted at school because of his terrible surname, which can also be interpreted as "virgin," but he'll soon have to get used to being teased in other ways... Mamori is kidnapped during exercise class and wakes up on the exotic island of Mermaid, stranded and under assault. Luckily, enigmatic fellow castaway Mirei Shikishima knows exactly how to take the lead—through a passionate kiss, Mirei unleashes Mamori's Exter transformation abilities, turning the innocent red-head into a battle-ready cutlass through the power of arousal.