The second half of that novel by this author consists of an autobiographical letter written by the Sensei to the unnamed narrator, explaining the former's decision to commit suicide.
Early in one work by this author, a character asks the narrator to consider what it means "to be tied down by long black hair", after insisting there is guilt in love. Later in that work by this author, a student caustically declares that anyone lacking spiritual aspirations is an idiot when his friend admits his love for the daughter of his landlady. After Okusan informs him of Ojosan's engagement to his roommate, K. leaves a note asking "Why did I wait so long to die?" in one novel by this author. The second half of that novel by this author consists of an autobiographical letter written by the Sensei to the unnamed narrator, explaining the former's decision to commit suicide. The title character of another work by this author drowns in a jug of water after becoming drunk. For 10 points, name this author of Kokoro and creator of the observer of Coldmoon and Waverhouse, the unnamed narrator of I Am a Cat. 
Early in one work by this author, a character asks the narrator to consider what it means "to be tied down by long black hair", after insisting there is guilt in love.
Natsume Soseki [or Natsume Kinnosuke; prompt on "Kokoro" until "The title character"; prompt on "Soseki" or "Kinnosuke"] 