What was the narrator's relationship with sensei in Kokoro?

The relationship between the narrator and Sensei, the central relationship in the story, is one of student and, literally, teacher, though a very unconventional one at that. From the very beginning of the story, even before we the readers become aware of Sensei's emotional depth and life experience, the narrator names him as Sensei, and so we listen attentively to what the man says, trying to understand him. In fact, the narrator himself instinctively realizes that Sensei is a teacher figure, even a father figure, for him, which makes him impulsively call Sensei 'Sensei'. As the narrator himself says, Sensei was not an obvious or good mentor in any usual way, especially in comparison to the university lecturers whom the narrator encountered as a student. A man who seems to live against the ideas of the time by squandering his talents in idleness, Sensei gives the narrator sincere advice in life of the sort that he does not find from his other teachers or his father.