Kokoro (こゝろ, or in modern kana usage こころ) is a 1914 Japanese novel by Natsume Sōseki, and the final part of a trilogy starting with To the Spring Equinox and Beyond and followed by The Wayfarer (both 1912).

One day, after finishing his usual swim in the sea, he takes notice of a man in the changing house who is being accompanied by a foreign guest, preparing to head for the water.

They set a date for a graduation celebration, only to have their plans put on hold by news of Emperor Meiji falling ill. As the weeks go by, the narrator's father gradually loses his vigor and becomes bedridden.

All are moved when news comes of the suicide (junshi) of General Maresuke Nogi, who takes his own life to follow his Emperor in death.

Stealing away from his father's bedside, the narrator opens the letter to find it's the previously promised accounting of Sensei's past.

As an only child, he inherits the family's considerable wealth, which his uncle steps in to help manage during the years over which, as previously planned, he pursues his education in Tokyo.

Sensei salvages what remains, arranges for the sale of his house and possessions, visits his parents' gravesite one last time, and turns his back on his home town, severing all ties with his relations.

After some time, he thinks to ask the widow, who treats him as family, for her daughter's hand, but still holds back for fear that the women are playing him just as his uncle had.

Sensei has a friend and classmate from the same hometown, whom he refers to simply as K.[a] K is the son of a Buddhist priest, but was adopted by the family of a prominent local physician who funds his study of medicine in Tokyo.

With the widow's approval, Sensei convinces K to join him as a second boarder, arguing that K's presence there will serve toward his own spiritual betterment.

Sensei is pleased with the improvement he's worked in his friend's demeanor but also begins to see K as a rival for the daughter's affection.

Sensing K's vulnerability, and at the same time seeking to serve his own interest, Sensei reminds K of his own words on discipline and servitude to a cause.

His betrayal of K, and K's death, continue to cast a shadow over his married life, yet he remains unable to burden his wife with his secret.

With the ending of the Meiji era and the passing of General Nogi, Sensei decides that he's outlived his time and must part from the world.

[8] McClellan traces the theme of seeking relief from isolation through Natsume's earlier works of The Gate and Kojin to its solution in Sensei's suicide in Kokoro.

Even though guilt comes into play, taking responsibility for one's actions and mistakes is paramount in the Confucian and Japanese ideology portrayed in the novel, and Sensei understands those traditions.

[citation needed] Sensei clearly feels responsible for K's suicide, displayed in his constant trips to the cemetery at Zoshigaya to visit K's grave, his belief that he is being punished by heaven,[9] or is destined for misery and loneliness,[10] his belief that he must never be, or can never be, happy,[11] because of this betrayal of K. Thus, as is often the case in Japanese culture (particularly in the Tokugawa period, but also certainly carried on beyond it), Sensei's suicide is an apology and an attempt to show penitence, or to do something about one's mistakes.

He is constrained by weakness, and has not the strength to hold to either those traditional Japanese values, or the new modern Western ones that were fast replacing them throughout the Meiji era.

Jun Etō attributes the focus on isolation in Natsume's work to a philosophical crisis which the author underwent while studying in London.

Takeo Doi provides a contrasting interpretation of the novel, in which the psychological dominates and which sees Sensei's life as a descent into first madness, then suicide.

[16] Translator Meredith McKinney elucidates the notion of a homosexual motive, saying "Kokoro tells the story of three young men whose hearts are 'restless with love' and of their emotional entanglements not only with the opposite sex but variously with one another.

The narrator is at an earlier stage in his own transition from a simplistic celebration of life in the opening pages to his own growing separation from mankind.

[21] This position is supported by Sensei's own statement (albeit in jest) that his suicide would be, "through loyalty to the spirit of the Meiji era",[22] while earlier in the book he had explicitly connected his isolation with the times he lived in: "loneliness is the price we have to pay for being born in this modern age, so full of freedom, independence, and our own egotistical selves".

[24] Sensei's suicide is therefore a recognition that the end of the Meiji era has rendered as anachronisms those who, like him, are torn between modernity and tradition.