The actor and painter explains why the world needs to see Minimata, the new film about the mercury poisoning scandal that W Eugene Smith helped expose

Like Cher or Madonna, Minami is a one-name wonder. “I have my French and Japanese family names,” the 34-year-old actor says over video call from a pink hotel room in Tokyo. “But ‘Minami’ is simpler.” She gives a single, decisive nod. “Just write ‘Minami.’” She chose the mononym at 13 when she featured in her first film, Battle Royale, a gory cult thriller about schoolchildren fighting to the death on an uninhabited island. “When I went back to school, everyone said: ‘Your arms are all bruised, you have scratches, what’s going on?’ They thought my parents were beating me.”

Even when telling a story like this with dark undertones, her manner is insistently perky, as though she doesn’t want the listener to misread her as dour. When I ask about her Battle Royale audition, for instance, she blithely recalls “walking into the room and there were 10 men, and they asked me if I could do a handstand, and two of the men held my legs against the wall to help me …” I must be grimacing because she breaks off from the anecdote to reprimand me lightheartedly: “Don’t make that face! It was all fine.”

Related: Minamata review – Johnny Depp attempts redemption in heartfelt look at disaster that struck Japanese town