Kenji’s fairy tale, “Porcelain berry and the Rainbow”, was adapted into “Marie Bron and the Girl”. This study focuses on the death of her younger sister Toshiko, which is considered one of the causes of the adaptation, and the differences between the two works. I would also like to pursue the changes in Kenji’s mental world that appear in these two works. “Porcelain berry and the Rainbow” was written in 1921, and “Marie Bron and the Girl” was adapted in 1926. Although the two works have largely the same content, the reason for revising and rewriting it is based on its connection to the death of her younger sister Toshiko in 1922 and examines the circumstances surrounding it. Kenji speaks of coexistence not only in the tangible natural world but also in the intangible world through the characters. In “Porcelain berry and the Rainbow”, he places importance on the recognition of the value of existence of everything, and in “Marie Bron and the Girl”, he pursues the value of a different way of life. Through the two works, Kenji’s mental world and its changes are explored through the characters’ language and the flow of the story. Kenji’s fairy tales cannot be explained through theory, but they use rich expressions that convey the author’s emotions to the readers. Among the works, Kenji’s view of the universe, which cannot be fully explained by modern science or physics, is depicted. This study found that the abstract claim in “Porcelain berry and Rainbow” that existence itself has absolute value is in line with the concept of the Pure Land Buddhism believed in by Kenji’s family. Meanwhile, in “Marie Bronn and the Girl”, which places value on the missionary work carried out by the girl, the importance of effort is shown metaphorically. The relevance of the adaptation was analyzed by pursuing Kenji’s inner world, outlook on life, and values that were changed by Toshiko’s death. In his first written work, “Marie Bron and the Girl”, which was adapted into “Porcelain berry and the Rainbow”, Kenji tried to express his feelings by writing about the changes in his spirit and the growth of his heart due to Toshiko’s death. Among the repeated lines of the characters in the work, there is a desire for an ideal in which all beings can coexist symbiotically. And the study focused on Kenji’s view of nature, which combines the truth of the universe and life energy.