Director Sunao Katabuchi has been planning and preparing for the film since 2012. In order to ensure the authenticity of the film, he made a special trip to Hiroshima and spent a lot of time studying historical details
. Due to insufficient funds, the producer launched a crowdfunding campaign on the crowdfunding website from March 9th to May 29th, 2015 with a target of 20 million yen (equivalent to about 1.184 million yuan), a total of 3374 people participated and raised 36.224 million Japanese yen (equivalent to about RMB 2.144 million)
. After the film was released, in order to raise the cost of the director to promote the film overseas, the producer launched crowdfunding on the official website, and reached the goal of 10 million yen (about 610,000 yuan) on the first day
.
Originally, director Sunao Katabuchi was going to make a 150-minute feature-length film. Due to financial problems, he decided to cut off 30 minutes, but he has been unable to give up the idea of "making a fantastic 150-minute version". The producer once said that if the box office exceeded 1 billion days Yuan, will fulfill his wish. When the box office reached 700 million yen in December 2016, producer Maki announced that the funds had been raised and an expanded version would be produced
.
