The first footage from Konstantina Kotzamani’s debut feature has just arrived, and it’s unlike anything else in this year’s selection. The Greek filmmaker has conjured something genuinely strange and irresistible: a dayglo fantasia about girls who train to become professional mermaids, and the one among them who learns that the costume is only the beginning. Set in a Japanese boarding school where teenage girls learn to hold their breath, perform for adoring crowds, and swim alongside sharks, the film follows 17-year-old Akame as she finds her voice, discovers first love, and ultimately undergoes a metamorphosis. It taps into something primal — the same childhood longing that made Daryl Hannah’s mermaid in  Splash  an icon, and that has fueled a real-world mermaid performance subculture ever since.…