Masato is an ordinary high school student, who is friendly and considerate to all around him. He also writes novels under the pen name "Kuroi." One day, a girl named Yamashita Miyu seeks him out, determined to force him to tell her the 'secret' in his novel. Miyu is obsessed with him, and she will go so far as to handcuff him to keep him from getting away from her! Masato's once-peaceful life will never be the same!

(Source: MangaHelpers)