Li Syaoran is a young boy from Hong Kong who becomes an exchange student in Sakura's class. If the nature of their relationship is not explained by that picture, I don't know what else to throw out there!
Having said that, their relationship has not always been so amiable. Syaoran is actually a descendent of Clow Reed (the creator of the Clow Cards), and he is sent to Sakura's school to bring the Clow Cards back to his family. He speaks down to her and refuses to call her by name, instead addressing her as "you". Even so, Sakura tries to be nice to the new student, but even she becomes frustrated with his belittlement of her. Eventually, Syaoran warms to Sakura's efforts and the two become friends - even going so far as to call each other by their first names.
It is not until a new exchange student named Eriol arrives that Syaoran truly relizes his feelings for Sakura; Sakura, oblivious to any possible deeper intentions of either boy, spends time with Eriol freely. Once boiling with jealousy at the attention the other is receiving, Syaoran understands how precious the relationship was and wants it back. However, this is not just a contest of wits or charm,a nd Eriol soon steps aside after revealing his true intentions: to test Sakura's powers and help her become the most powerful magical force.
Through the trials against the cards, Sakura begins to see Syaoran as a pillar in her adventures; something consistent and strong that will always be there when she needs it. She admits this to Syaoran further along in their friendship by telling him she feels safe when he's there (thus causing him to blush up to his ears). Despite the embarrassment, Syaoran is content in his role. Having such an understanding makes their relationship surprisingly mature for their age, and neither Sakura or Syaoran would have it any other way.
