Kingdom Hearts and The Legend of Korra are in the same boat. Sora and Riku are incredibly loving towards each other and have a degree of comfortability with each other that would easily convert into a love relationship. However, since they're princely rulers they can't get close to anyone other than their subjects- especially not when one is trying to save the world while the other is trying to stop it.
However, this doesn't mean that they aren't able to feel affection for one another. King Mickey once said that there was a time when Sora could've been taken away from Pluto but wasn't because he knew that Riku needed him. Also, during the final battle with DiZ, when all hope seemed lost, both princes go above and beyond what anyone should be capable of to show how much they care for one another. With their hearts destroyed by then though so whatever feelings they had before that wouldn't be returned to.
Finally, after the events of Kingdom Hearts III it's revealed that Xemnas has returned and is looking for his children. When he finds out that Riku is alive, he uses his powers on him and makes him forget about his love for Sora. This causes Riku to go on a quest to remember who he really is so he can rescue his brother. He eventually does so and destroys Xemnas once and for all.
Sora's buddy and fellow Keyblade wielder, Riku, is a friend and fellow Keyblade wielder. He is one of the few Keyblade Masters, and he will very certainly play a significant part in Kingdom Hearts 3, maybe as a playable character. This essay will go through the events leading up to Kingdom Hearts 3, so be aware that there will be spoilers for all prior games.
Riku first appears in Disney's Hollywood Studios during the "A View From Above" show, where he is seen battling Maleficent's minions. After the battle, Riku meets with Sora and asks him to join his quest to find his friends Donald and Goofy, who have been taken to Castle Mickey. When they arrive at the castle, it is revealed that Pete has found them and that they are being held captive by Tetsuya Nomura himself. With no choice left, Riku uses his keyblade to free them from their bonds once again and the four of them head off into space to stop Ansem/Zeus from destroying worlds with a giant cannon.
In the final game, Riku plays an important role after being transformed into a heartless. His goal is to find a way to return to human form while helping Sora fight against Heartless throughout the various worlds. At the end of the game, Riku manages to restore light to a world called "Talia", which causes him to revert back to human form.
Riku didn't care for her. He was simply envious of Sora and desired to be the hero. That entailed being the one to rescue Kairi in order to outdo him. However, when it came time to save her, he was too late. When he arrived at the scene, she had been rescued by Jack Sparrow. Despite this, he continued on his quest to become a hero.
Later on, after the events of Kingdom Hearts II, Riku encounters Sora again. This time, however, he is the leader of an army of Disney characters who have joined forces to fight against Maleficent. After defeating her, Riku realizes that he has fallen in love with Sora and wants to be by his side forever. But since this isn't possible, he decides to go on living his life to the fullest while waiting for his friend to return home.
In Kingdom Hearts III, it is revealed that Riku still lives in Castle Town with his friends until they are called upon again by Donald to help save both worlds from destruction at the hands of Ansem/Ventus. This time, however, Riku refuses to leave his post even if it means sacrificing himself. Knowing that there's no way he can stop what's about to happen, he chooses to face it head on so that he can give Ventus the ending he deserves.
Riku was envious of Sora because he wished to be more like him, which isn't always a negative thing. So Riku uses his newfound understanding to become a better and stronger person for Sora and himself. By DDD, he has realized that he and Sora need one other and that they strengthen each other just by being themselves. Also, it is revealed that before he met Sora, he had been friend with someone else who looked exactly like him. When this other guy found out about Sora, he became obsessed with him and even tried to kill him multiple times. Finally, when Riku realized what he had done, he decided to put an end to his jealousy and left the world of gaming forever.
Sora has helped many people including Riku himself. Even after all that has happened between them, they still love each other as friends. If anything, it can be said that Sora has made Riku a better person.
Riku has grown a lot over the series. Because of this, he will always be my favorite character. He's more powerful than Sora, most likely because Riku can manage his darkness (he's got the whole dark and light thing going on). He'd accepted himself for who he was. Also, when you consider everything that has happened to him, it isn't hard to see why he would want to protect everyone else from suffering like he has.
Sora is still my favorite character, but I do think Riku is better now. They're both great characters with good hearts!