Mousecracker

Mousecracker is the slash ship between the Mouse King and the Nutcracker from the Nutcracker and Barbie fandoms.

The Nutcracker and the Mouse King - E.T.A. Hoffmann
After being given to young Marie Stahlbaum as a gift, the Nutcracker was haunted by the eventual arrival of the Mouse King. In the dark of the night, the vicious rodent invaded the bedroom of the innocent girl, trying to get to his enemy. The Nutcracker however sprang into action after Marie happened to break the glass door of her toy cabinet by accident. He summoned the toys to aid him in battle, though the others worried for him for it seems that one arm and one leg were broken. Despite him staying on track to defeat the Mouse King, his injury left him incapable of doing anything but giving commands during the battle, the Mouse King quickly overwhelmed him by simply disabling his cannons with his own soldiers. But when the Mouse King cornered the Nutcracker, Marie was so distraught that she quickly reached for the next weapon she had, a slipper and happened to throw it right at the Mouse King. This forced his army into a retreat, with Marie fainting due to the cut she received on her arm when breaking the glass door.

Nobody believed Marie when she told the story of the battle between Nutcracker and Mouse King, but her godfather Drosselmeyer tried to cheer her up by telling her the origins of the Nutcracker: He was the nephew of another man named Drosselmeyer, who was chosen to lift Princess Pirlipat's curse by cracking a very rare, hard-to-crack nut, giving her the kernel to eat with his eyes closed and taking seven steps backwards without stumbling. However, since Nutcracker happened to step on Madam Mouserinks, who had cursed Pirlipat in the first place, Pirlipat's curse was lifted, but the Nutcracker was cursed instead for his trouble. In her dying breath after being impaled by the Nutcracker's heel, Madam Mouserinks foretold that her son the Mouse King shall be the one to kill the Nutcracker as revenge.

So the Mouse King returned for a rematch against the now-repaired Nutcracker, pressuring Marie into giving up her precious sugar dolls for him to eat, else he'll turn the Nutcracker into splinters with his teeth. Under tears, Marie complied, and this procedure went on for several nights. But then the Nutcracker finally spoke to Marie, telling her that he can take care of himself, she should only provide a sword so he could slay the Mouse King. Marie lended one from her brother and the next night, the Nutcracker returned to her with the Mouse King's seven crowns as proof for his victory.

The Nutcracker - Piotr Ilyich Tchaikovsky
Unlike the original story, Clara manages to kill the Mouse King by throwing her slipper at him the first night, when he was trying to attack the Nutcracker. To show his gratitude, the Nutcracker would take Clara to the Land of Dolls, sometimes having the backstory with the Mouse Queen told on location.

Fanon
Most people seem to ship the Nutcracker with the Mouse King as a "What if they were friends?" scenario, rather than actually seeing any real chemistry between them. Despite the Mouse King often being played by older actors, the original book implies that they are actually the same age, giving fans a bit more of a reason to believe that they could settle their differences.

In particular, fans of the 1990's Warner adaptation questioned why the Nutcracker still felt obligated to kill the Mouse King, despite hints that the villain could've been redeemed. This may have been because the movie failed to mention that killing the Mouse King was necessary to break the Nutcracker's curse in the original story, implying that the Nutcracker had to do it even if he didn't want to.

Fandom

 * FAN FICTION