Searches for "La Petite Sirène" on ok.ru often confuse Jean-Claude Brisseau’s 1980 live-action drama with the popular 1975 Toei anime series (often titled "Marina" in French) which was broadcast during the 1980s. The anime is noted for its faithful, tragic adaptation of the original tale, whereas the 1980 French film is a modern psychological drama, both of which can be found via ok.ru searches using specific French titles. To find the live-action film, you can check on Видео Le Secret de la Petite Sirène | OK.RU Le Secret de la Petite Sirène. Одноклассники La petite sirène (1980) - Plot - IMDb

For years, this film was geographically and politically locked. Produced by Barrandov Studio in Czechoslovakia, it circulated primarily in Soviet bloc countries. When the Iron Curtain fell, the film fell with it—buried under the weight of Western animation and the logistical chaos of post-Communist copyright transfers. This is where OK.ru enters the narrative.

The Ending: Instead of dying, she dissolves into sea foam but is transformed into a "daughter of the air," granted a chance to earn an eternal soul through 300 years of good deeds.  Why it stands out 

. It is not an animation, but rather a live-action interpretation of the themes from Hans Christian Andersen’s classic fairy tale. Encyclopedia.com Film Overview