Unavaatu

Unavaatu is the slash ship between Unalaq and Vaatu from The Legend of Korra fandom.

Canon
It is not known exactly how Unalaq first came into contact with Vaatu, but he learned of him while most of the world had forgotten about him, Raava, and Wan. Unalaq soon decided that the Spirit World should not be cut off from the physical world and that Vaatu should not be trapped in the Tree of Time. Unalaq eventually tricked his niece, Avatar Korra, into opening the spirit portals. Unalaq began secretly travelled to the Spirit World to speak with Vaatu.

If one of the spirit portals was open, Korra was presumed dead before the other was opened. Unalaq tried to get his children to help him open the other one, but it did not work. Unalaq apologized to Vaatu and told him that he had failed him. Vaatu calmed him down and told Unalaq that he had not failed because Korra was still alive and in the Spirit World. Unalaq followed Vaatu's instructions to capture Jinora and force Korra to open the other portal.

Unalaq later revealed that his true plan was to use the coming Harmonic Convergence to permanently bond with Vaatu and become a Dark Avatar. Vaatu was on board. Vaatu managed to escape the Tree of Time, and though Korra tried to keep them apart, the two eventually combined and became the Dark Avatar. The two of them were very powerful and even managed to extract Raava from Korra and kill her. After that, they attacked Republic City until Korra arrived. She and Jinora were eventually able to bring Raava back from inside Vaatu and cleanse them with spirit healing. Because they were permanently combined, Vaatu and Unalaq died together.

Fanon
Unavaatu is a very popular ship in the Legend of Korra fandom. It gained a following as soon as it was revealed that they were working together, and became even more popular after they fused to become the Dark Avatar. Some ship this as a parallel to Waava, since both ships involved one working with a spirit and the two eventually becoming permanently combined.

Fandom

 * FAN FICTION
 * Unalaq/Vaatu tag on FanFiction.net
 * Unalaq/Vaatu tag on FanFiction.net

Trivia

 * "Unavaatu" also refers to the gigantic form of the Dark Avatar.