Okada Michiyo (later Nagayo Michiyo) is a female writer who is known to have been used by Tayama Katai as a model for the young female live-in student the protagonist novelist secretly falls in love with in Futon. This article examines the obscure works she wrote before she married Nagayo Shizuo, as well as the letters exchanged between Katai and her until just after the publication of Futon. The result of this investigation reveals how the male mentor (Katai) and the female student (Okada) fought over the literary treatment of Michiyo's romantic affair. After Michiyo became romantically involved with Nagayo, her parents forced her to leave Tokyo and return home to Hiroshima. She then wrote fictionalized versions of her relationship with Nagayo, and used some parts of Katai's letters in her stories. Elsewhere in his letters, Katai was critical of Michiyo's subjective narrative. While he forbade her to continue fictionalizing her own affair, Katai himself used her affair in writing Futon. This leads us to consider this famous novel a work of sexual harassment : Katai robbed Michiyo of the authorship of her own story, and meticulously concealed her identity as a woman capable of exerting literary authorship over her own affair.