“Kokoro” is a novel by Japanese author Natsume Soseki, published in 1914. It is the story of the friendship between the narrator, “I” and his honored mystery old man, “Sensei”, which explores man’s nature through Sensei’s confession. As seen in the very first sentence of the story, the narrator always calls the old man, Sensei in respect. The story reveals that Sensei also has a big trust in narrator by sending his testament to “I”(narrator) in the hopes of preventing the narrator from going through what Sensei had gone through. In Sensei’s letter, Sensei tries to say that he does not deserve narrator’s respect because he betrayed his friendship with dear friend “K” by choosing woman who also was beloved by K. Sensei believes “ love is sin”