Pakku and Kanna's relationship first started while they were both teenagers and living in the Northern Water Tribe. At some point, a marriage was arranged between Pakku and Kanna as this was the tradition of the Northern Water Tribe. Pakku actually did love Kanna and carved her a betrothal necklace as this was a part of the tradition. However, Kanna did not seem to love Pakku back and did not wish to be forced into a marriage. She eventually left for the Southern Water Tribe because she was tired of the sexist customs. Pakku was upset by this and never married anybody else. Kanna settled in the south and married someone else. She has a son named Hakoda and eventually two grandchildren as well but her husband presumably passed away at some point.
Several decades passed and Kanna's granddaughter Katara arrived at the Northern Water Tribe in order to learn waterbending along with Aang. Pakku would not train her because northern customs only allowed women to learn the healing aspect of waterbending. Katara fought Pakku but he still refused to train her. However, he eventually saw her necklace and realized that she was Kanna's granddaughter. Pakku remembered that she left because of their sexist customs and finally decided to train Katara. Pakku eventually left to help rebuild the south. He and Kanna eventually got married after all and Pakku carved a second betrothal necklace for her.
Kakku became a rather popular avatar ship once the pairing became canon in the four-part finale of the series. However, this ship is still often overshadowed by the ships involving the younger and main characters, especially with other ships becoming canon at the end of the finale. Some fans try to bring more popularity to this ship because they feel that it is under-appreciated. However, Kakku does not have a large amount of fan art or fan fiction.