“Frantz,” by gay French filmmaker François Ozon, is a black-and-white costume drama set in 1919 Germany. A loose remake of the Ernst Lubitsch drama “Broken Lullaby,” this handsome romantic melodrama, opening March 31 at Ritz Theatres, has Anna (Paula Beer) mourning her fiancé Frantz (Anton von Lucke), who was killed in the war. One day, she spies Adrien (Pierre Niney) at Frantz’s grave and befriends him. When Adrien visits Frantz’s parents, Hans (Ernst Stötzner) and Magda (Marie Gruber), he recounts stories about their friendship. However, Adrien eventually reveals his relationship with the dead man to Anna, and the dynamic between them changes.