Karin

is a former subordinate of Orochimaru who assisted him in his experimentations and was left in charge of one of his bases while he was away. She has red eyes, matching hair color, and an unusual hairstyle: her hair is short and unkempt on one side and long and combed on the other a sign of a fluctuating personality; Karin will at times appear tough and in control, and at other times will appear flirtatious. Karin's name means is made up for the kanji meaning "fragrance or perfume" and sulfur. It is also a homonym for the fruit 'quince'.

Background
Little is known of Karin's past other than her status as a jailer at one of Orochimaru's bases. However, Sasuke had at some point noticed her at the time of his defection and had decided to use her in "Snake" long before rebelled against Orochimaru. Unlike the rest of the team, Karin was indeed loyal to Orochimaru, going as far to refuse the release Orochimaru's prisoners even after his defeat.

Personality
Karin usually appears as tough and prone to violent outburst, her usual victim being Suigetsu. However she, like many in Konoha before her, has a huge infatuation with Sasuke Uchiha, to the point of fanaticism. For example, when "Snake" was resting in a village to take care of the wounded Sasuke after his battle with Deidara, Karin planned to use a drug on Suigetsu and Jugo to put them to sleep so she could have her way with Sasuke, and planned to keep one of his battered, sweat-drenched shirts for herself.

Abilities
Karin's special ability allows her to track specific individuals through chakra, seen when she is able to discern that Jugo is not among a crowd of prisoners through the standard concentration pose for molding chakra. It also allows her to pick up chakra from long distances and notice changes in an individual's chakra. Kakashi Hatake surmises that Karin is a particularly skilled chakra-sensing ninja, as she is not only able to tell that his group is approaching, but can also sense how many of them are present and that one is a dog. Karin also has the ability to heal others by letting them bite her arm, and suck in her chakra, when Sasuke  bit her arm (after being injured by the eight tailed beast) his wounds healed. It should also be noted that she had other bite marks on her arms meaning probably this isn't the first time she used this ability.

Hunt for Uchiha
Sasuke Uchiha recruits her as a member of Snake. While Sasuke admits she may be troublesome, he also notes that her special abilities make her useful. She also seems to have a liking for Sasuke, implying to Sasuke that a team consisting of the two of them would be much better than one with Suigetsu Hozuki or Jugo. Once the team is completed, Sasuke sends "Snake" out in multiple directions to try and locate Itachi Uchiha. While on the search, Karin passes Sakura Haruno, though the two do not acknowledge each other. After Deidara's suicide explosion, the rest of the team regroups and takes Sasuke to an inn to recover. When Karin went out for supplies, including a drug that would allow her alone time with Sasuke, she sensed the 8-Man Squad approaching, and warned the team. It was her plan to use Sasuke's old clothing as a means to distract the Squad from catching them. When they finally got back on Itachi's trail, Karin stayed behind with Suigietsu, Jugo, and Kisame as Sasuke went a head to battle Itachi.

Karin, and the rest of "Snake" was present with Sasuke and Madara Uchiha when he renamed the team "Hawk" for their new goal; the utter destruction of Konoha.