In 171 ASC Unalaq and his children arrived at the Southern Water Tribe for the Glacial Spirits festival. They were greeted by many people, including Tonraq and his family. Upon greeting his brother, Tonraq addressed him in a harsh manor, prompting the same response from his brother.
Unalaq then took a walk with Korra, his brother and Tenzin throughout the area of the festival. He commented on his beliefs that the Spirituality the south had once had was dissolving. After Tonraq said that he didn't think it was a big deal, Unalaq brought up the fact that ships in the South were being attacked, which surprised Korra. Unalaq then offered to teach her about spirits, but Tonraq interrupted saying that Korra had been busy learning about airbending and would not be able to take him up on his offer.
That evening, Unalaq attended a feast thrown in his honor, but Unalaq said that the current feast paled by far in comparison to how things used to be, where tribal chiefs would communicate with the spirits as they glowed and danced in the sky. Unalaq then offered again that he become Korra's spiritual mentor, but Tonraq again declined for her, much to Unalaq's frustration. He said that it was only fair she travel with him since every Avatar before her had traveled to learn, whereas Korra had spent most of her life cooped up in the Southern Water Tribe on the requests of Tonraq and Tenzin, to Korra's surprise.
Unalaq then made a speech declaring that the South was soon going to enter Spiritual decay and that it was up to him to do something to change that. He said that the spirits attacking ship were proof of these troubles and that it should be his duty to make things right.
That night, a dark spirit attacked the area where Korra and several of her friends were sleeping. They all attempted to fight it off, and their efforts were later joined by Tonraq and Tenzin but to no avail. However Unalaq then entered and performed a complex waterbending maneuver that caused the spirit to disappear.
Seeing how Unalaq was the only person who could fight spirits, Korra decided her training under Tenzin was over and she would take lessons under Unalaq since that was what seemed the most proficient way to go.