If Kyoshi was defined by action, then her predecessor was defined by inaction. Avatar Kuruk initially had grand plans to further unite the Human World following the progress of Avatar Yangchen. But shortly into his career his plans were dashed. Kuruk was the first known person to come in contact with a dark spirit, and the encounter forever altered his life, leading to the slow corruption of his spirit.
Everything that we know about the Avatar has to do with duty. These men and women have to unite the people of different regions to maintain world order. They have to protect the benders. They have to communicate with the spirits. But what if there was an Avatar who did none of those things and instead shirked his responsibility? That’s exactly what Avatar Kuruk did. Instead of performing his duties he turned to women and booze to ease his pain. Whether his inaction was a result of laziness, fear, or apathy, it eventually led to the loss of his fiancée, his own life, and the safety of the world at large.
We know what it looks like when an Avatar succeeds, but seeing one fail would be just as interesting. As both series touch on again and again, the responsibility of the Avatar is a massive burden for anyone. Following someone who simply decided not to take it on would be fascinating at least for a season and would add depth to Aang and Korra’s maturity.