Tonraq met Senna at some point after he arrived at the Southern Water Tribe. Tonraq was previously a general and the next in line to become chief at the Northern Water Tribe until he was banished. Following his banishment, he moved to the Southern Water Tribe and met Senna. They eventually fell in love and got married. Their goal was merely to live a simple life with one child. They had a daughter named Korra (who they raised as an only child), but she was born around the time that Aang passed away and was eventually discovered to be the next Avatar.
Tonraq and Senna had merely desired to live a simple and secluded life until they discovered that their daughter was the avatar. Their dreams of a simple life ended, but they still loved their daughter with all their hearts and remained happy together. After many years of her training, they finally allowed Korra to leave her secluded compound. However, she would return many months later for the Glacier Spirits Festival.
Tonraq was eventually involved in a rebellion against his brother Unalaq and a meeting was held at their house. After other members of the rebellion attempted to kidnap and assassinate Unalaq, Tonraq and Senna were both wrongfully arrested. Senna was released of her charged but Tonraq was sentenced to death. However, Unalaq convinced the judge to change it to a life sentence in prison. Still, Senna was devastated and ended up crying in Korra's arms at home because her husband was being forced to spend his life in prison. They visited Tonraq in prison who convinced them not to bust him out, but Korra later did so anyway after realizing that everything was set up by Unalaq.
While Korra was gone and seeking help, Tonraq and the other members of the rebellion eventually attacked the Northern Water Tribe forced and the former was captured by Unalaq. Senna was upset and informed Korra of this when she returned. Korra eventually managed to free Tonraq and had Asami take him to Katara for healing. Senna stayed by her husband's side throughout the events of Harmonic Convergence. Following the fall of Unalaq, Tonraq was elected as the chief of the Southern Water Tribe so he and Senna moved into the Southern Water Tribe palace.
Senraq is a popular pairing in the fandom due to the fact that they are married and the parents of Avatar Korra. This pairing especially became popular after information for Book Two: Spirits was released and it was revealed that Tonraq is actually from the Northern Water Tribe and related to the current chief while Senna was always from the south. A lot fans especially loved the fact that Tonraq met her after his banishment and wanted to live a simple life with her until they had the avatar as a child.
KorraKorra is the only child of Tonraq and Senna. She is the current avatar and successor of Avatar Aang. Korra was a bending prodigy and was able to bend water, earth and fire by the time that she was just four-years-old. Korra always had trouble with air, but she eventually learned it as well after temporarily losing her bending in Republic City. Korra is also the last avatar of the first cycle and the first of the second cycle because Raava was temporarily extracted from her and destroyed, and while she managed to save Raava and recombined with her, her connection to her past lives was forever lost.