Sasuke and Karin first met during the Chunin Exams. Sasuke was with Konoha while Karin was with Kusagakure and both were a part of different teams. However, when Karin was separated from her team while in the Forest of Death, she was attacked by a large bear and Sasuke saved her. It turned out that Sasuke was looking for a scroll which Karin did not have but she still got a good look at him and blushed.
Over two years later, Sasuke left Konoha to train with Orochimaru while Karin was taken from her village to join him as well. When Sasuke absorbed Orochimaru, he added Karin to his team "Hebi" and told her that he needs her. She constantly moved very close to him and he often asked her to give him some space. They later went on a mission to locate Sasuke's brother Itachi.
As a medical ninja, Karin was able to tend to Sasuke's wounds whenever he was injured. She was also able to have him bite her in order to receive some Chakra and heal himself. Karin actually enjoyed this whenever he bit her. Sasuke later battled Danzō while Karin attended. Danzō managed to capture Karin and held her hostage in hopes of stopping Sasuke. However, he simply pierced the both of them with a Chidori Current and explained that Karin became a burden by being kidnapped.
Karin was later saved and healed by Sakura who took her back to Konoha for interrogation. She ended up crying and sympathizing with Sakura because she could see her love for him as well. During the Fourth Shinobi World War, Karin managed to escape. She reunited with Sasuke on the battlefield and he apologized to her for nearly killing her. They were separated for a while and Karin panicked when she could not sense Sasuke's Chakra.
Years after the end of the war, Karin continued to work at Orochimaru's hideouts. Sasuke eventually married Sakura and had a daughter named Sarada with her. Karin delivered Sarada and stored her umbilical cord. She was content with Sasuke being happy even though he did not end up with her and also provided her with a pair of glasses. There was a brief period of time when Suigetsu falsely led Sarada into believing that Karin is her real mother so she scolded him for this and explained everything.
SasuKarin is a very popular pairing in the Naruto fandom and is one of the most popular het ships involving Sasuke next to only SasuSaku. Many fans ship this due to Karin's crush on Sasuke and the fact that they were always allies even while Sasuke was an enemy to Konoha. SasuKarin fans were disappointed when SasuSaku became canon but got their hopes up during Naruto Gaiden when they were falsely led into believing that Karin is Sarada's mother. The fans were even more disappointed when this turned out to be a red herring. SasuKarin usually rivals the SasuSaku and SuiKa pairings.
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