In the Itachi Pursuit Arc when Team Hebi enter Konoha, it is revealed that Sakura and Karin had passed by eachother at some point; although at that time, they did not acknowledge one another.The two do not meet again until the Five Kages Summit Arc. When Sakura is finally able to locate her former teammate, she finds him about to kill Karin. She was able to save her some time by driving his attention towards her. She claims that she wanted to join him. Seeing this, Karin thinks to herself that Sakura must also love him but the moment quickly turns into bitterness when Sakura is asked to kill Karin in the process. As her former teammate prepares to attack her, Karin is able to warn her by muttering for him to stop. Sakura is then saved by her sensei and takes Karin to a safer location to heal her.
As Sakura heals Karin, Karin silently comments to herself that she shouldn't be sympathising with the enemy and silently pleads for Sakura to stop crying. She soon finds herself crying with Haruno Sakura and curses herself; You're the enemy..I don't want to sympathise with you.. so.. so don't.. don't cry like that in front of me..! Damn it.." Once Karin was in better shape, she warns Sakura about her former teammate and asks what was she willing to do. However, a emotionally-unstabled Sakura doesn't respond and leaves to return to the battle despite Karin's warning.
When Naruto arrives and they return back to Konoha, he asks who Karin was. Sakura then replies that she was a member of Sasuke's group to where Karin denied.
Naruto Gaiden: The Seventh Hokage and the Scarlet Spring:
During a conversation with Suigetsu, it is revealed that Karin helped deliver Sakura's child, Sarada , in her[Karin's] hideout and kept their cord for future cases, revealing the two's friendship.
- Karin was able to notice Sakura's feelings for Sasuke right away.
- Sakura healed Karin despite knowing she was an enemy.
- Revealed in Naruto Gaiden, Sakura and Karin became friends. Following this, Karin was also the one who delivered Sakura's daughter, Sarada.
Karin about Sakura - Chapter 483:
- "She's...an old friend...she must love him too..."
Karin to herself about Sakura - Chapter 484
- "You're the enemy.. I don't want to sympathise with you.. so..so don't..don't cry like that in front of me..! Damn it.."
Karin to Suigetsu about Sakura - Chapter 710:
- "There's a thing such as friendship between women. --- Connections, they come in many forms."
Among the Fans
SakuKarin is actually a very popular Yuri Couple in the Naruto Fandom. This couple is most likely supported due to both being the female teammates of Uchiha Sasuke and as both love/care for him. They both share a very similar personality as well as beating on one of their teammates when rather annoyed. It can also be said that they are both healers. It's a rival couple towards SasuSaku, SuiKa, and NaruSaku.