Sakura is the fan-made name for the couple consisting of Sakaki and Kagura. They have a fairly friendly relationship, even though Sakaki is far from as much of a jock as Kagura first thought when she met her. This is a yuri coupling.
In canonSakaki's and Kagura's canon interaction is mostly initiated by Kagura, who grew interested in Sakaki when they participated in sports events together, always competing for the top spot. When Kagura joined Class 3 in her second year, she approached Sakaki and told her she had always wanted to have a talk with Sakaki since she had heard Sakaki was much like herself. However this was not entirely true, since Sakaki was not interested in sports like Kagura, but merely naturally athletic. Kagura was very surprised that Sakaki did not even remember her when the events had meant so much to Kagura.
She declared Sakaki to be her rival, which surprised her, and often tries to challenge Sakaki to various competitions. But Sakaki lacks the interest to put any real energy into it. Kagura also tried to compare her test scores to Sakaki's, but she was scared off when she saw Sakaki's impressive results, unaware of how smart she was.
They frequently have company on their way from school. This is how Kagura found out about Sakaki's "cat problem", as she saw Sakaki getting bitten many times. Kagura attempted to drive off the cats who tried to attack Sakaki, but the latter did not like being ignored by the cats. Kagura invited Sakaki to join the swim team, but Sakaki explained that she did not want to, causing Kagura to call her a lone wolf and Sakaki to imagine a cute little wolf cub in her head instead of a cool-looking one.
Besides seeing her as a rival, Kagura often tries to be Sakaki's friend. Sometimes she ends up hurting Sakaki's feelings instead because of their differences in temper, Sakaki being more sensitive and thus taking some of Kagura's comments too seriously. An example is when Sakaki announced plans to move from home and get her own cat. Kagura said that it was alright that she didn't have one, because even if she did, it would hate her. However, Sakaki seemed happy along with the others upon finding out that Kagura had made it into college.
This is not as popular as some of the other pairings, but it still has fans and fanfics have been written about it. In the pairing's fandom, many people assume that Kagura may have a crush on Sakaki, considering how interested in the latter she is.