Kobukuro's Kobuchi Kentaro used to be a salaryman for four years between the ages of 18 and 22 and even became a supervisor at 21 before he became a musician. As such, he tapped on his past experience to write the song titled "Kokoro" (Heart) which describes how to live on when the heart and body are not in sync. During those tough days when he was busy with visiting clients, although there were happy things he experienced, he also found that it was not fulfilling and felt as if his soul was not with him at work. During that period, he began performing live on the streets of Sakai, Osaka, as a form of therapy for himself and met his singing partner Kuroda Shunsuke there. As such, when Kobuchi saw the movie, he was reminded of his past memories thus giving birth to the song.