The film is based on the book "Shima no Hate" by the late Shimao Toshio who was a navy lieutenant sent to Kagoshima's Kakeromajima towards the end of WWII and later became a writer after the war ended as well as his wife Miho's book "Umibe no sei to shi". The movie uses the Shimaos as a model to describe how Toe (Mitsushima) falls for a man named Saku in the last days of the war. Toe is a teacher at a national school who meets Saku who is newly posted to the island and becomes drawn to him when she sees him learning how to sing the island's songs while being slightly intoxicated. However, when the couple finally get together, Toe is torn by her love for Saku who is awaiting orders to go out to battle.
Mitsushima who was born in Okinawa, revealed that her family's roots are actually in Amami Oshima so going there for the filming of this movie was a very different feeling as compared to filming in Tokyo. Hearing the familiar dialect and songs and seeing the dances there was a fascinating experience for her as it seemed to bring her back to the days she was in Okinawa before she went to Tokyo at the age of 13. With regard to her character Toe, Mitsushima described her as someone who lives for love and seeks a place of her own. In that sense, she felt that she could identify with Toe's thinking.
As for Nagayama who is playing a person who existed in real life for the first time, he revealed that he had asked fellow actors for advice but he realised that there was more he could do to play this type of roles. Luckily, the island where they were at for the filming contained many references to Shimao so it helped him to fill in the missing bits and pieces needed for him to play this character.
As this was also the first joint public appearance of Mitsushima and Nagayama since they were reported to have started dating in May 2016, Mitsushima revealed an interesting episode during the filming when she was asked by the children on the island if Toe was going to die for the man she loved. Upon hearing an affirmative answer, the children were quick to say that she shouldn't do that for such a man which made her very amused and she was quick to clarify that this remark wasn't directed at Nagayama. When asked about rumours of them having broken up, Mitsushima gave an OK sign with a huge smile on her face while Nagayama also smiled but did not say anything as they left the event venue's stage.
Sources: Nikkansports / Eiga.com