It's been well over 50 years since the Sada Abe Incident happened, but mentioning the very name of Sada ABE (阿部定) still causes 50% of the Japanese populace to blanch. The story has an obvious American parallel, but I won't cut to the chase quite yet...

Our protagonist didn't have a particularly happy life: raped by a university student at a young age, she was kicked out of her wealthy family and forced to make do on her own. As employment opportunities for women in pre-war Japan were pretty limited, she became a maid with, according to some sources, a sideline as a prostitute. (No, she was not a geisha!).

In 1936, when she was 31, she was hired by Kichizo Ishida (石田吉蔵), who managed a small inn in Tokyo with his wife. Within a week Sada and Kichizo had hit it off, but Mrs. Ishida soon figured out what was going on and fired Sada. Sada retreated to a machiai (read: love hotel) called Masaki (満佐喜, a pun translating more or less to "help in filling with joy") and invited Kichizo to join him. He did, and the two proceeded to have sex, non-stop, for the next six days, not stopping even when the maids tiptoed in to bring food.

On the morning of May 18, 1936, Sada came downstairs and told the maids that she'd be going out for a while. Around noon, one of the maids went in to bring Kichizo lunch, but soon dropped her tray in shock -- lying on the floor was Kichizo's corpse, strangled with a sash and covered with blood. Written in blood on his left thigh were the characters 「定吉二人」 ("Sade and Kichi, we two"), similarly incribed on the sheets was the phrase 「定吉二人キリ」("Sada and Kichi, we two alone"), and carved on his left arm was the character for "Sada" (定). The source for all this blood? Kichizo's penis had been neatly amputated.

Three days later, Sada was apprehended in Takanawa and brought to the police for questioning -- the full interrogation transcripts (in Japanese) are available at the URL listed below. Some of Kichizo's personal effects were found in Sada's luggage, but his manhood was still missing; when inquired about its whereabouts, Sada produced a wrapped bundle containing his member from her bosom. It was, she said, the one thing that held for her the fondest memories.

As for means and motive, Sada told the police that she could not bear the idea of any other woman having Kichizo. During their sex marathon they had practiced erotic asphyxiation, Sada wrapping her sash around his throat in order to get his penis to dilate again, so she had killed him simply by not letting go.

Sada was duly charged with murder and corpse mutilation, which she did not contest, but the third charge was too much: she refused to be labeled a hentai-seiyokusha (変態性欲者), or "sex pervert". Calling up her legal counsel for the first time, she managed to get this changed to merely ijou-seiyokusha (以上性欲者), "oversexed person". She was sentenced to six years in prison (an astonishingly lenient sentence) and, after her release, kept working as a maid and waitress until her death from natural causes at the age of 64.

In the West, the story of Sada Abe is best known via the 1976 movie "In the Realm of the Senses", known as Ai no Corrida (愛のコリーダ) in the original -- and yes, that corrida is the same as the Spanish word for a bullfighting ring. Filmed outside Japan to avoid its strict obscenity laws, the highly controversial movie featured, among other things, explicit penetration and fellatio. The story has also been reworked less explicitly as "The Abe Sada Story" (実録:定阿部, 1975) and just plain "Sada" (1988).

References

http://www.asahi-net.or.jp/~gr4t-yhr/abesada0.htm
http://www.midnighteye.com/reviews/abesada.shtml