The rivalry between Sora and Riku has been a through-line leading up to Kingdom Hearts 4, with their childhood competitions have transitioned from friendly to toxic and back again. However, in the last major installment, the push and pull of these two protagonists had to take a back seat in order to finish off the Xehanort Saga as the universe-ending stakes were front and center.
With the initial stakes of Kingdom Hearts 4 from the perspectives of Sora and Riku being as simple as getting back home, this could allow for the rivalry dynamic to step back into focus at the start of the new journey. This could also allow the mid-game or end-game turn where the stakes are raised to cause a more concrete whiplash for the story than it did in Kingdom Hearts 3. Most interestingly, this is a similar dynamic to how Dream Drop Distance handled its story.
When Sora and Riku's Rivalry Was at Its Best
The rivalry between Sora and Riku tracks all the way back to before the first Kingdom Hearts, with flashbacks showing how they would spar against each other to impress Kairi. However, this era of Sora and Riku competing with each other is what eventually led to the major conflict between them in their original adventure, with a bitter jealousy causing the two to fight on more than one occasion. It was a compelling dynamic to make Riku out as an antagonist at first, but their competitive edge was at its best in Dream Drop Distance.
One of the latest spin-off titles that is entirely necessary to follow the story is Dream Drop Distance, and it includes one of the best dynamics between Sora and Riku since the original. Although they are both aware of the need to earn the Mark of Mastery, the two still take advantage of what they assume to be lowered stakes in the sleeping worlds to turn their combined test into a competition. It's a positive version of their rivalry that turns into friendly competition, with both Sora and Riku pushing each other to succeed, but also being excited about each other's victories. This culminates in a wholesome moment at the end where Sora celebrates his friend's victory, without focusing on whether he lost himself.
Heartless in the Realm of Fiction to Reignite the Friendly Rivalry
At this point in the series, it is the friendly rivalries with no hint of animosity that makes for the best dynamic between Sora and Riku. Unfortunately, this wasn't really the case for how the story played out in Kingdom Hearts 3 though, as the two were mostly separated and working on completely different objectives for the majority of the game. This separation then had some knock-on effects with everything that led up to the end-game too, as Sora rarely interacts with anyone outside Donald and Goofy. It is one of many aspects of Kingdom Hearts 3's story that adds to the feeling that Sora is meandering through his adventure.
Taking a step back to Dream Drop Distance, Square Enix has the perfect opportunity to continue to show a positive and healthy competition between Sora and Riku. With both protagonists now so far removed from antagonizing each other, Kingdom Hearts 4 has another golden opportunity to show these two fuel their rivalry and remain the light-hearted heroes they've both grown into across the series. This could reflect both on Sora as a character and the player, with Riku being the competitor that can be beaten in order to pull the most satisfaction out of each encounter. With the Kingdom Hearts series often shying away from ranking systems during general gameplay, some healthy competition could also help open the door for a higher skill ceiling.
Kingdom Hearts 4 is in development by Square Enix.