Valkyrie Drive: Mermaid

Mamori Tokonome, a 16-year-old high school student, is frequently teased at school due to her surname, which can be read as "virgin." During a gym class, she is kidnapped and ends up on Mermaid Island, where she soon finds herself in a life-threatening situation. There, she meets Mirei Shikishima, who saves her life by unlocking Mamori's Exter transformation abilities through a passionate kiss.