The ending of The Wheel of Time Season 3 paves a broader future for Rand al'Thor and his companions while continuing the storylines spanning four books. In the season finale, Rand demonstrates his astonishing power in the Aiel Waste, officially confirming himself as the legendary Car'a'carn, shattering Couladin's false porpagate of the Shaido religion. However, despite Rand's ability to summon rain in the desert and display immense power, Couladin seems unlikely to give up and be defeated easily.
Next, Rand's mission is to continue fulfilling his destiny as the Dragon Reborn: to find the legendary sword, Callandor, which is hidden within the massive fortress known as the "Stone of Tear." While The Wheel of Time Season 4 may cover this plot point, the storyline might differ from the original novels. Though this is just my speculation, I believe the series may make adjustments to the story, giving Couladin a more significant role in the battle at the "Stone of Tear."
The plot of this season draws inspiration from The Shadow Rising, the fourth book in The Wheel of Time series, which deviates slightly from the novel's chronological order. At the start of the season, Moiraine suggests Rand go to the Stone of Tear to find Callandor — the sword guarded by the Dragon Reborn — but Rand refuses, insisting on traveling to the Aiel Waste to rally the Aiel people. This change creates a gap in the original story, which may be filled in Season 4.
In the third book, The Dragon Reborn, Rand and his companions journey to the "Stone of Tear" and engage in a fierce battle with Ba'alzamon and Ishamael, two of the Thirteen Forsaken, ultimately seizing the Sword of Callandor. While this scene has not yet been depicted in the series, it will likely be featured in Season 4. Moreover, with Couladin's debut, he will most likely continue to play an important role in the next season.
In The Dragon Reborn, the Aiel help Rand capture the city of Tear, and Couladin will likely be involved. Although Rand seemingly dispelled all doubts about his identity as the Car'a'carn in the Season 3 finale, Couladin is unlikely to readily abandon his claim to that title. In fact, with Lanfear's support, Couladin may take the initiative in the battle at the Stone of Tear, attempting to reclaim Callandor. Such a confrontation will not only strengthen Rand's leadership among the Aiel but also present him with more challenges to overcome.
In The Fires of Heaven, the fifth book in The Wheel of Time series, Couladin returns to challenge Rand's rule. After Rand proclaims himself the Car'a'carn, Couladin leads his loyal Aiel forces to sack the city of Cairhien. Rand then travels to Cairhien personally, waging a major battle to retake the city. In the end, Couladin is killed by Mat in the fighting, and Rand emerges victorious, becoming the new ruler of Cairhien. However, if my memory serves me correctly, Couladin's story may reach its climax as early as Season 4, culminating in a showdown at the Stone of Tear.
The battles of Tear and Cairhien are both crucial events in the original novels, so it is unlikely they will occur in the same season. A more reasonable approach would be to merge them; perhaps Couladin will appear in the Battle of Tear, condensing the two battles into one major conflict. While this speculation may seem a bit far-fetched, based on the plot's development, the TV series may choose to delay the events of The Fires of Heaven until Season 5, with Season 4 continuing the story of The Dragon Reborn. Nevertheless, such a significant adjustment to the chronological order might make the plot feel somewhat unnatural.
The Wheel of Time TV series appears to want to advance the plot faster than the original novels, hence introducing Couladin's character earlier. After all, the original series consists of 14 novels with an enormous amount of content, and there is uncertainty about whether the show will run for that long. Based on Season 3, it seems that Rahvin will be one of the main villains in Season 4. At the end of Season 3, Rand rejects Lanfear, and she decides to ally with the Forsaken, beginning to discuss with Rahvin how to stop Rand. She also hints that Callandor might be of great value to Rahvin, a suggestion that piques his interest, and he questions whether Lanfear is truly ready to oppose Rand for this.
It is possible that the series will completely eliminate the character of Ba'alzamon, having Rahvin take his place in the show. Although Rahvin does not participate in the battles at the Stone of Tear and Cairhien in the original novels, the groundwork laid in Season 3 indicates that he will likely play an important role in Season 4. Following this trend, Rand will face unprecedented challenges, not only competing with Couladin for Callandor but also confronting the new threat posed by Rahvin.
As the plot of The Wheel of Time Season 4 unfolds, there is no doubt that Rand al'Thor will face the most difficult test of his life so far.