Before the likes of Naruto and Sasuke or Hinata and Kageyama, there was the "Tensai" Hanamichi Sakuragi and Kaede Rukawa. The dynamic between these two not only works to drive Slam Dunk's narrative, but fosters their development and growth, both as individual characters and as teammates. In this regard, Sakuragi and Rukawa's rivalry was, and still is, the gold standard for what it truly means to be rivals in a shonen manga/anime series.
Basketball, a Girl & the Birth of a Rivalry
At the start of Slam Dunk, basketball, for Hanamichi, is a means to an end; that end being the heart of Haruko Akagi. On the flip side, for Rukawa, basketball is and always has been everything. Despite their different motivations, ultimately the goal for both men is to become a great player. The controversy lies in the fact that Haruko actually has a crush on Rukawa due to his immense talent and skill.
This dynamic, while built on a simple premise, is highly effective. The love triangle operates in a sort of rock-paper-scissors manner: Hanamichi likes Haruko, who likes Rukawa, who likes basketball. The only way for this balance to be broken is for one of the parties to tip the scale in his or her favor, and Hanamichi, ever persistent, is just the man for the job. Hanamichi is determined to surpass Rukawa at basketball in order to gain Haruko's adoration, and despite being fundamentally inept, possesses enough raw talent to do so. Rukawa's disinterest in everything but basketball makes him the perfect foil for Hanamichi in this regard, as his laser focus on the sport allows his character to constantly grow stronger regardless of Hanamichi's efforts or Haruko's feelings.
As Hanamichi grows as a player and his skills are acknowledged by Haruko, he comes to truly love the sport. This brilliantly reverses the roles that Rukawa and Hanamichi play in each other's lives, as Hanamichi's goal of becoming the best now places him in the same race as Rukawa. Differing goals meant that Rukawa could never truly view Hanamichi as a rival until this point, as he was never actually competing for Haruko's affection. Hanamichi's decision to chase the title of Best In The World positions him directly in the way of Rukawa's dream, transforming their competition into one that is no longer one-sided. This is the beauty of their rivalry: both Rukawa and Hanamichi never stagnate as people or players, which means that their opposition is in a constant state of evolution as well.
Rivals & Teammates: A Different Kind of Victory
Both teammates and rivals are directly responsible for each other's growth. As Rukawa and Hanamichi hold both of these positions in each other's life, their responsibility for each other's growth is magnified. This is why Rukawa takes it upon himself to show Hanamichi no mercy in their one-on-one session, as giving anything but his best would be disrespectful to himself, Hanamichi and their efforts up to that point.
Winning a practice one-on-one is far from a decisive victory for these two, though, as their shared dynamic changes the way that their battles resolve. The growth of either Hanamichi or Rukawa directly improves the strength of Shohoku as a whole, and is thus beneficial to both parties whether they like it or not. As the two aren't in direct opposition to each other, the definition of victory changes for Rukawa and Hanamichi, with defeat beautifully manifesting itself as an acknowledgment of each other's strength.
This is why the high five they exchange at the end of their match against Kainan Auxillary is promptly followed by the two of them turning away from each other in disgust; acknowledging each other is also both men losing to each other. The term "losing" is a loose one in Slam Dunk, as a defeat for Hanamichi and Rukawa comes at a cathartic moment of total victory against the reigning champions.
Even though Slam Dunk ended a long time ago, if the story had continued past the two character's freshman years Rukawa and Hanamichi's rivalry would only have grown more intense. In the final moment shared by these two in the series, both stare into the distance with the future of their basketball careers in mind.
Following this moment, Rukawa and Hanamichi silently part ways and continue training. Hanamichi still loves Haruko, Haruko still loves Rukawa and Rukawa still loves basketball. The difference, though, is that Hanamichi now loves the sport too. One "defeat" or high five isn't enough to end this eternal rivalry, and that's why it's one of shonen manga/anime's best.