M in the Motif Index stands for tales about Ordaining the Future. It includes judgments, vows, oaths, prophecies, bargains, promises, and curses - things such as "M211. - Man sells soul to devil." Some of them go into a little more detail than others... Case in point:
M149.4. Quarreling prince and princess vow that if they are married he will desert her on the wedding day and she will make him eat boiled rice and thin broth for six months
(This is typically the type of motif that should not have its own number. I don't think there will ever be another tale that fits this description.)
The title of this tale is also pretty interesting: Katmanush, or The human being who was made of wood. It is a Bengali story. The motif pretty much describes the beginning: A prince and a princess haggle for the same item on the market one day, and they get into such a fight that they mutually curse each other out. The prince swears that if they ever got married, he would leave her right away; the princess swears that she would make him so ill he can only live on jhol bhaat for six months.
Of course a few years later their parents arrange a marriage for the two (without them knowing about it). True to his oath, the prince walks away on the wedding day and never looks back.
Some months later the prince's mother hires a very peculiar new servant: It is a woman made of wood, but she walks and talks like a living being. She insists on never cooking, and sleeping in her own room, but in all other regards, she works just like a regular servant.
One day when everyone is away from home, the princess - because she is the one inside the wooden doll, duh - comes out of her shell to sit on the roof. The prince returns unexpectedly and sees her. The whole palace is turned upside down, looking for the "beautiful woman" he had glimpsed - but there is no one there but the wooden doll. The prince get so lovesick that he is about to die.
The god Shiva reveals to the prince's sister that his life can be saved if the wooden woman cooks for him for six months, and sleeps in his chambers. The queen and the sister beg Katmanush to do it for the prince; after a whole lot of begging, the wooden woman agrees, but only if she can cook alone, and sleep with the lights off.
Six months pass by. The princess feeds thin broth and boiled rice to her husband for six months, as she had once promised. As she does, they slowly fall in love with each other. At the end of the six months, she reveals herself to him - and they lock themselves in the bedroom for a looong time, and the prince emerges "healthy and cheerful."
How is that for a love-hate romance?...
(Read the original text here.)
M114.3. Vows taken on holy swine
M114.5. Taking oath on cowdung
M115.1.1. Oath so heavy it dries up stream; oath so great it splits the rock in twain; oath so violent it makes the tree wither
M119.7. Oath by placing hand on genitals
M142. Vow never to carry a woman
M166.3. Vow to kill anyone who touches his beard
M205.1.2. Cat witness to betrothal punishes violator
M211.6. Man sells soul to devil for visit home in boat that sails through sky
M242.1. Mortal fosters fairy child to prevent destruction of crops
M301.15. Mountain in human shape prophesies whole family’s death
M304. Prophecy from enigmatical laugh
M364.2. Prophecy: remission of tax through endeavor of saint
M429.1. Release from curse by burning vomit