edited the summary of Sputnik Sweetheart Saturday, September 18, 2010.
The heroine of the novel is an aspiring author named Sumire, who falls in love with an older woman, Miu, who appears to like Sumire for certain qualities, though she has no time for Sumire's aspirations and ideals. The third character is the unnamed narrator, an elementary school teacher, referred to twice by Sumire only as 'K', who is in love with Sumire, though Sumire does not requite his feelings.
While Sumire is an emotional and spontaneous individual who often appears to be a misfit in society, "K", the narrator, is a person who has through sheer force of will moulded himself into another person, one who integrates seamlessly into the wider society and culture around him, and the transition leaves him emotionally stunted and unable to express his feelings. When Sumire is also, through her interaction with Miu, forcibly shaped into a person other than she is, the transformation is neither permanent nor successful, and Sumire disappears without ever being found or seen again while holidaying with Miu in Greece, with tragic, haunting consequences for Miu in particular.